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NSRDS—NBS 44

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NSRDS

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The Radiation Chemistry

of Gaseous Ammonia

i
NATIONAL BUREAU OF STANDARDS

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1974

The Radiation Chemistry

of Gaseous Ammonia

Donald B. Peterson

University of San Diego

San Diego, California 92110

Prepared at the

Radiation Chemistry Data Center,

Radiation Laboratory,

University of Notre Dame,

Notre Dame, Ind. 46556

U.S. DEPARTMENT OF COMMERCE, Frederick B. Dent, Secretary

NATIONAL BUREAU OF STANDARDS, Richard W. Roberts, Director

Issued February 1974
Library of Congress Catalog Number: 72-600106

NSRDS-NBS 44

Nat. Stand. Ref. Data Ser., Nat. Bur. Stand. (U.S.), 44, 40 pages (Feb. 1974)

CODEN: NSRDAP

(C) 1974 by the Secretary of Commerce on Behalf of the United States Government

U.S. GOVERNMENT PRINTING OFFICE

WASHINGTON: 1974

For sale by the Superintendent of Documents. U.S. Government Printing Office, Washington, D.C. 20402

(Order by SD Catalog No. C13. 48:44). Price 70 cents Stock Number 0303—01164
Foreword

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Reliable data on the properties of matter and materials is a major foundation of scientific and technical progress. Such important activities as basic scientific research, industrial quality con--

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to support American science, industry, and commerce is vitally fulfilled.

Richard W. Roberts, Director

iii
Preface

This report is one of a series of data publications on radiation chemistry; the aim of the series

is to compile, evaluate, and present the numerical results on processes occurring in systems which

have been subjected to ionizing radiation. Various kinds of data are important in radiation chemistry. The quantities which were measured first were the observed radiation yields or G values (molecules formed or destroyed per 100 eV). Various indirect methods based on G values have been used to determine yields of transient species and relative rates of reactions. The spectral properties (optical,

electron spin resonance) of transients have provided a direct method for their identification, and rates of the very fast reactions of transients which occur in irradiated systems have been measured directly

by spectroscopic methods. Conductivity and luminescence methods have also provided a means of

measuring properties of transients and their kinetics. Some reactions which occur in irradiated systems

have also been studied by other methods, such as photochemistry, electric discharge, ultrasonics, chemical initiation, electron impact, etc. The emphasis in these publications is on the data of radiation

chemistry, but where other pertinent data exist, they are included.

The data of radiation chemistry are voluminous; thousands of systems have been investigated.

As a result there are certain collections, e.g. rate constants of particular types of reactions or certain

properties of transients, for which tabulations of the data are considered essential, but for which

critical assessment of each value is impossible. On the other hand, certain systems and properties

have been studied so extensively that critical examination of these data is desirable and timely.

Authors of this series of data publications have been asked to evaluate the extent to which the data can be critically assessed, to describe their criteria for evaluation, and to designate preferred values

whenever possible.

iv
Contents

Page Foreword iii Preface iv

1. Introduction 1

2. Mechanism 2

2.1. Elementary processes 2

2.1.1. Elementary processes involving ions and excited neutrals 2

2.1.2. Free radical processes 5

2 . 2 . Yields of intermediates 6

2.2.1. Neutral species 6

2.2.2. Ionic species 10

3. Product yields 10

3.1. Static systems at ~ 20°C and ~ one atmosphere -. 11

3.2. Effect of various parameters 13

3.2.1. Dose 13

3.2.2. Dose rate 13

3.2.3. Temperature 14

3.2.4. Pressure 16

3.2.5. Electric field 19

3.2.6. Flow rate 19

Appendix 1 . Selected properties of species involved in radiolysis of gaseous ammonia 20

Appendix 2 . Additives used in studies of ammonia radiolysis 22

References 24

List of Tables

2 . 1 . Elementary processes 3

2. 1 . 1 . Yield of intermediates in radiolysis of gaseous ammonia 7

2.2.2. Yield of H atoms 8

2.2.3. Primary yield of H2 9

3.1.1. Product yields from radiolysis of gaseous ammonia with various radiations under static conditions at ~ 20°C and ~ 1 atm 11

3.1.2. Product yields for radiolysis with 60 Co — y at ~ 20°C and ~ 1 atm 12

3.1.3. Yields for radiolysis with alpha particles at ~ 20 °C and ~ 1 atm 12

3.2.1. Effects of dose 13

3.2.2. Effects of dose rates at ~ 23°C 14

3.2.4. Effects of pressures 17

A. 1 . 1 . Properties of neutral species 20

A. 1 . 2. Properties of ionic species 21

A.2.1. Additives: Binary mixtures 22

A.2.2. Additives: Ternary mixtures 24

List of Figures

3.2.3. 1 . Variation of G(— NH3 ) with temperature at dose rates less than 1019 eVg

- 1 s

_1 15

3. 2 . 3. 2 . Yields of H2 , N2 H4 and N2 versus temperature 16

3.2.4. Variation of G(H2 ) and £(— NH3 ) with pressure at 23° C — 18

v

The Radiation Chemistry of Gaseous Ammonia*

Donald B. Peterson

University of San Diego, San Diego, California 92110

H 2 and N 2 are the only significant products of radiolysis of gaseous ammonia under static conditions

at dose rates less than about 10

19 eV-g

_1

s *; and G(H2 ) = 5.0 ± 1.0 and G(N 2 ) = 1.7 ± 0.3 for irradiation

at 20°C and pressures near one atmosphere. Yields do not appear to depend significantly upon LET

(linear energy transfer); and they are independent of dose up to at least 8 x lO^eV/g. In static systems

at dose rates 3= 10

26 eV-g'V, and in flow systems, N2 H4 is also a product. At dose rates less than 10

19 eV-g

_1

s *, G(— NH3 ) increases markedly with temperature and reaches a plateau value of about 10 at temperatures near 150 — 200°C. At very high dose rates ( 3= 10

26 eV-g 's *) G(-NHj) increases significantly at higher temperatures (value depends upon dose rate) and G(-NH3 ) does not appear to be leveling off at the highest temperature studied (460°C). In both dose rate regions the increase in G(-NH 3 ) is attributed primarily to the increasing importance of NH3 + H —

NH2 + H2 with increasing temperature. G(-NH3 ) also appears to increase with decreasing dose rate. However, the effect is less pronounced than the effect of temperature, and the experimental evidence

is not unequivocal.

NH and NH2 have been observed spectroscopically in pulse radiolysis of NH3 and such studies lead

to g(NH) = 0.4. However, this value of g(NH) is low because of errors in dosimetry. g(NH 2 ) was not obtained directly because the absorptivity of NH2 was not available. A number of additives has been

employed in attempts to determine primary yields of other species involved in radiolysis; however,

results with different additives and from different laboratories are in good agreement only in the case

of g(H 2 ) (0.7 — 0.8) and g(NH4

+

) (3.3 — 3.9). The best value of g(H) appears to be 10.4 ± 0.6; and this is the preferred value. g(NH2 ) is obtained from the material balance, g(H) + 2g(H2) = g(NH2 )+2J§'(NH). The preferred value of g(NH) is 0.75, i.e., g(NH) = g(H2 ) and this leads to g(NH 2 ) = 10.4.

Key words: Ammonia; chemical kinetics; data compilation; G; g; gas; radiation chemistry; rates; review.

1. Introduction

This compendium provides a comprehensive summary of data relevant to the radiation

chemistry of gaseous ammonia. A complete mechanism for the radiolysis of ammonia cannot be

written at present. However, probable contributing processes are discussed in some detail and the

supporting evidence is examined critically when possible. Specific rates and/or energies of

activation for these elementary processes are given when available but in general such data are not critically evaluated. Properties such as bond energies, ionization energies and electron

affinities are tabulated for the major intermediates (app. 1). Such data have for the most part been

taken from authoritative reference sources and are presented without critical comment. Preferred

values are given for yields of both products (sec. 3) and intermediates (sec. 2.2.1 and 2.2.2).

Throughout the text and tables references are cited by Radiation Chemistry Data Center serial

number; in many cases, the authors, or first author only, are included with serial number for easy

identification of the work. When only a first author is cited, that name is followed by periods

corresponding to the number of co—authors, as Nishikawa..68—0505. The bibliography is a listing

of references by serial number; the first two digits of the number represent the year, so that the

*This is a data review prepared for, and in cooperation with, the Radiation Chemistry Data Center of the Radiation Laboratory, University of Notre Dame, Indiana 46556. The Laboratory is operated under contract with the Atomic Energy Commission. The work of the Center is supported in part by the National Bureau of Standards,

Office of Standard Reference Data.

1
listing is approximately chronological. The literature has been covered through the first half of

1970; however, a few selected papers published later are included.

Symbols and Units

Radiation yields are in units of molecules per 100 eV and are designated G(X) when X is a reaction product. G(-NH3 ) represents molecules of ammonia converted to reaction products per

100 eV of energy absorbed. Various conventions have been used for reporting yields of

intermediates. In this review such yields (in molecules per 100 eV) will be designated by use of

the symbol g. Other symbols used to designate properties, and the units in which values of the properties

have been reported in this review, are listed below. A list of conversion factors is also included

when non-SI (Systeme International) units have been used.

£>, bond dissociation energy, kcal/mol.

Em , activation energy, kcal/mol.

E.A., electron affinity, eV.

AH( °, standard heat of formation, kcal/mol.

I.P., ionization potential, eV.

k, specific rate, second order processes in

dm3 mol_1 s“l. P, pressure, atm or torr. P.A . , proton affinity, eV.

t, temperature, °C

<1>, quantum yield.

Conversion factors:

1 kcal = 4.184 kj

1 atm = 101 325 N/m2

1 torr = 133.32 N/m2

1 eV = 1.602 x 10- 19 J 2. Mechanism

2.1. Elementary Processes

Because the relative importance of various elementary processes involved in radiolysis of

gaseous ammonia depends upon such factors as dose rate, temperature and pressure, it is not

possible to write a single mechanism which will be applicable under all conditions. The significant

elementary processes that should be considered in mechanisms for radiolysis of gaseous ammonia

are summarized in table 2.1.

Formation and reaction of NH4 are not included. There is some evidence for this species from mass spectrometric studies (67-9004) and its possible formation via NH3 + H + M in

photochemical systems has been discussed (44—7000, 34—7002). Simic and Johnson (68—0659) have

considered it as a possible intermediate in radiolysis of NH3

. At this time, however, evidence is very limited.

2.1.1. Elementary Processes Involving Ions and Excited Neutrals

There is considerable experimental evidence in support of the general assumption that ions

and excited neutrals produced in reactions (1) and (2) (table 2.1) lead principally to NH2 and H;

NH and H2 are also produced but in relatively small yields. (See table 2.2.1.)

2
Table 2.1. Elementary processes

Reaction Specific rate* Comments

(1) NHj VA—» NHj+ + e

- MV+ NH2 + + H + e" —

NH+ + Hj + e

Accounts for ~ 97% of total ionization at 2 x 10

_7 torr for 100 eV e”; relative abundances are NH3 +

: NH2 +: NH+ = 100.0: 40.9: 4.5 (66-0298).

(2) NH3 AMr-> NH3 * — NH3 * represents totality of electronically excited states produced.

(3) NH3 * — NH2 + H Only primary process in photolysis when

k > 160 nm (69-7017, 68-7168, 62-7002,

62—0132). NH2 has been obs. spectrophotometrically in pulsed radiolysis (71-0169).

(4) NH3 * NH + H2 — In photolysis (4) accounts for about 12% of

(5) NH3 * -* NH + 2H primary dissociation 147 nmb (64-7003)

and 14% at 123.6 nmb (62-0132).

g(4) = 0.64e (68-0051).

NH observed spectrosocopically in pulse

radiolysis; g(NH) s 0.4 (68-0101). Also observed spectroscopically in photochemistry at k < 160 nm (67-7484, 63—6002,

63-0149, 62-7002).

(6) NH3 * + NH3 - 2NH3 Importance of (6) depends upon lifetime of excited state. Spectral and photochemical

evidence indicates that excitation between

217 and 166 nm leads to predissociation

(35-9001, 64-7008).

(7) NH/ + NH3 NH/ + NH2 6-11 x 10" d k7 decreases with increasing translational energy of ion (70—0563).

(8) NH2 + + NH3 -» NH3 + + NH2 1.1 x 10" (66-0298, 63-0150);

2.4 x 10u

(70-0563) —

(9) NH2 + + NH3 - NH4 + + NH 3.9 x 10 11 (66-9068, 67-9079);

6.5 x 10u

(70-0563) ka /k9 depends upon translational energy

of ion (70—0563).

(10) NH+ + NH3 -» N2 H2 + + H2 1.8 x 10

9 (66-0298)' —

(11) NH/ + e~ —> NH3 + H (1.5 ± 0.3) x 10“ (71-0002).

(See also 66—0201).

g(NH4 +

) = 3.9 estimated from studies with SF6 as additive*. NH4 + accounts for ~ 99%

of + ions at 1 torr in radiolysis with 100 eV e~ (66-0298).

(12) NH/ + e' - NH2 + H2 Limiting value of G(H2 ) in presence of H-scavengers leads to upper limit of ~ 0.8

for g(12)*. Studies with CC14 indicate

S(12) = 0.1

b

. (12) NH/ + e -^NH2 + 2H At normal temperatures and pressures (12')

is endothermic by ~ 40 kcal because of solvation of NH4 + (69-0326, 67-0546).

(13) NH2 + H + M - NH3 + M ~ 1.2 x 10

l ° (63-9010)*

1.8 x 10

10 (71-0216)*

1.2 x 10" (71-0169)

Pseudo—second order > 1000 torr (71-0169).

(13') NH2 + H - NH + H2 ~ 2.9 x 10

9 (71-0216)* Exothermic by 14 kcal.

(14) NH2 + NH2 + (M) N2 H4 + (M) ~ 2.5 x 10

9 (64-7002)* ~ 1.8 x 10

9 (71-0216)*

Pseudo—second order above ~ 0.45 torr (63—9010). N2 H4 is significant product in flow systems (67-0271) and in static systems at ^ lO^eV-g'V1 (68-0101, 69-0272) See also 71—0169.

(15) NH2 + NH2 -> NH + NHS 4.6 x 10*(64-7002)iJ

; 5 x 10* (71-0216)* —

(16) NH2 + N2 H4 - NH3 + N2 H3 109 exp(-7,000/RT) (65-9044)k —

(16') NH2 + H2 -> NH3 + H Endothermic by 0.1 kcal. Failure to observe dose dependence indicates (16') unimportant

under usual conditions (see section 3.2.1).

(17) NH + NH3 -* N2 H4 1.0 x 10

10 (68-7214)1 —

(17') NH + NH3 -> 2 NH2 — Exothermic by 14 kcal.

3
Table 2.1. Elementary processes - Continued

Reaction Specific rate* Comments

(18) NH + NH —> N2 H2 * N 2 + H2 7 x 10 n

(68-0101)“; 5 x 10

10 (71-0216)' —

(19) NH + N 2 H4 -* NH2 + N2 H3 10

11 exp(— 10,000/RT) (65-9044)k —

(20) NH + NH2 + (M) N 2 H3 + (M) — Exothermic by ~ 73 keal.

(21) NH + H + (M) —> NH2 + (M) — Exothermic by 90 keal.

(22) H + N 2 H4 ^ H2 + N 2 H3 3.5 x 10® exp(—2000/RT) (62-0131)" Hydrazine has been used as a radical

(22') H + N2 H4 ^ NH3 + NH2 10

10 exp (-7000/RT) (65-9044)

k scavenger in NH3 (See table 2.2.2).

(23) H + NH3 ^ H2 + NH2 4.1 x 10

10 exp(- 13,700 ± 600)/RT

(65-0555)°

Values of 4 x 10

9 exp(— 10,500/RT) and

8 x 10

7 exp(— 7200/RT) have been calculated from kinetic analysis of yields from

pulse radiolysis of pure NH3 at very high dose rates (71—0216).

(24) H + H + M^H2 +M 1.4 — 9.3 x 10

9 dm6 mol 2 s

1 when M = H2

. p Specific rate should be higher for M = NH3

.

(25) N 2 H3 + NH2 -> N2 H2 + NH3 — Estimate k2S = k H (65—9044).

k Exothermic

by ~ 50 keal.

(26) N2 H3 + H ^ N2 H2 + H 2 — Very fast (65—9044). Exothermic by ~ 50

keal.

(27) N 2 H3 + N2 H3 -* 2 NH3 + N2 & 3 x 10

9 at 150°C (62-0131)" May involve intermediate formation of tetrazane (N 4 H6

). q

(28) N 2 H3 + N 2 H3 N2 H2 + N 2 H4 k2Jk27 = 4 (70-7065); k27 >k2s (62-0131 ) n No obvious reason for contradictory

specific rate data. 1

(29) N2 H2 ^ N2 + H2 — Exothermic by ~ 49 ± 5 keal.

(30) N 2 H2 + N 2 H2 ^ N2 + N2 H4 — 65-9048

a. Unless otherwise indicated specific rates are in units of dm3 *mol

- 1 s

-1 and apply to temperatures near 25°C.

b. Based on limiting 4>(H 2 ) in presence of C 2 D4

.

c. CCU reduces G(H2 ) to 0.64 CCU assumed to scavenge both e— and H and thus (4) is only significant source

of H2 in NH3 -CC14

. (See sec. 2.1.1.)

d. Values reported are 6.0 (66-9068, 67-9079), 7.8 (66-0298), 9.0 (63-0150) and 10.9 (70-0563) in units of 10 11 dm 3 mol *s U

e. See also 63—0150.

f. See table 2.2.1.

g. See table 2.2.3.

h. Based on difference between G(H2 ) for NH3 + CC14 (see c above) and G(H2 ) from NH3 + C3 H6 (68-0051).

i. Determined by following decay of NH2 absorption following r.f. discharge through NH3

. Based on limited data and subject to uncertainties in absorptivity of NH2

.

j. At 2000 K, k ls = 2.5 x 10

10 dm^moU's-1 (63-0167); fc 14 = k l5 has also been reported from studies at room

temperature (absolute rate data not reported) (67—9109).

k. From analysis of the overall energy of activation of decomposition of N2 H4 on the basis of an assumed

mechanism involving (16).

l. Determined by kinetic spectroscopy in flash photolysis of NH3. m. Upper limit. Based on kinetic spectroscopy in pulse radiolysis of NH2 ; & 18 = 10

11 dm3 -mol 's

1 at 2000 K

(63-0167).

n. H atoms from microwave discharge flowed into N2 H4 vapor; reaction followed by mass spectrometry; temp.

range 25° to 150°C.

o. Also, ^23 = 104 dm3 mol 's

1 at 150°C and = 10—15 keal/mol (62—0131).

p. Values reported are 1.35 (68-5013), 3.4 (64-0288), 5.0 (38-9001), 5.5 (35-0002), 8.5 (34-0005), 8.9 (63-9014),

9.3 (61-9008) in units of 10

9 dm6 -mol”2 s

_1

. See also 65-9041, 67-9108 and 70—9010. Bennett and Blackmore

(68-5013) give a critical comparison of specific rates of H + H with H2 as third-body.

q. N4 H6 -* NH3 + NH=N-NH2 ; HN=N-NH2 <—> NH2 -N=NH; N3 H3 ->NH3 + N2 (70-7065, 54-9005).

r. Conclusion that k%? > k.28 is based on simple observation that NH3 and N2 in 2:1 ratio are only products when H

atoms flow into N2 tU (see n above). Ar2 s/A: 2 7 = 4 is based on a more complicated analysis of isotopic nitrogens

from reaction of H atoms with isotopically labeled hydrazines.

s. Estimated from collision theory.

t. Value calculated by kinetic analysis of product yields from pulse radiolysis of NH3 on basis of an assumed

mechanism.

4
Photochemical studies indicate that (3) is

(3) NH3 * -» NH2 + H

the only dissociation process at wavelengths greater than 160 nm (ref. in table 2.1). At shorter

wavelengths (4) and (5) also occur, however reactions (3) and (5) account for 80% of the

dissociation.

(4) NH3 * NH + H2 (5) NH3 * -» NH + 2H

The spectra of both NH2 (71—0169) and NH (68-0101) have been observed in pulsed radiolysis.

Primary positive ions from (1) undergo rapid ion-molecule reactions (7) — (10) and are thereby

converted almost exclusively to NH4 + (66—0298). The relative importance of possible modes of

neutralization of NH4 + (11), (12), and (12') has been investigated by addition of electron

scavengers. In pure ammonia, NH4 +

is neutralized by e~ since negative ion formation is negligible

(66—0298, 34—9002). In the presence of electron scavengers, NH4 +

is neutralized by the negative

ion formed in the scavenging process.

Nishikawa and co-workers (67—0263, 68—0051) have studied the system NH3 - CC14

. They

assume CC14 scavenges electrons in a dissociative attachment that leads to CC13 and Cl

-

, and that

neutralization of NH4 + with Cl

- yields NH4 C1. Because CC14 also scavenges H atoms, the limiting

value of G(H2 ) in the presence of CC14 should be the primary yield of non-scavengable H2 from

processes other than (12).

(12) NH4 + + e

- -> NH2 + H2 Comparison of this limiting yield of 0.64 with the total non—radical yield of 0.75 (see table 3.2.1)

leads to the conclusion that g(12) — 0.1. Neutralization of NH4 + to give NH2 and 2H (12') is endothermic by about 40 kcal (69—0326, 67—

0546) if, as seems reasonable, NH4 +

is solvated at normal temperature and pressures (68—0032,

66-9067, 64-9015). Thus, it appears that neutralization of NH4 + in pure ammonia proceeds

almost exclusively by reaction (11). In support of such a conclusion, Gordon, Mulac, and Nangia

(71—0169) have found that the initial concentration of NH2 measured spectrophotometrically, is unchanged when SF6 is added to NH3

. Gordon, Mulac and Nangia (71—0169) also conclude from the comparison of results for pure

NH3 and NH3 — SF6 that 45 percent of the hydrogen atoms are produced by ion—neutralization as opposed to dissociation of excited states. This can be compared with the results of Nishikawa and

co-workers (67-0263, 68-0051) who reported that approximately 42 percent of the hydrogen (H2 ) is the result of ion—neutralization. The latter estimate is based upon a comparison of hydrogen yields

from NH3 and NH3 — N2 0. It is assumed that ion—neutralization does not produce hydrogen

atoms in the presence of N2 0; and thus, the reduction in G(H2 ) by addition of N2 0 is taken to be

the yield of hydrogen from ion—neutralization. The two estimates are not necessarily directly

comparable because the former refers to hydrogen atoms while the latter refers to H2

.

2.1.2. Free Radical Processes Many important details of the mechanism by which H, NH2 and NH lead to observed products

are uncertain because of the lack of good specific rate data for many of the possible elementary

processes.

Evidence from radiolysis of NH3 in the presence of radical—scavengers indicates that most of

the observed yield of H2 results from processes involving free radicals. Non—radical processes

yield only about 0.8 molecule of H2 per 100 eV (table 2.2.1). At temperatures near 20°C radical sources of H2 include reactions (13'), (22), (24) and possibly (28) followed by (29). At higher

temperatures (23) is also important (see sec. 3.2.3).

5
N2 H4 is produced by combination of NH2 radicals but the observed yield is negligible in static

systems except at very high dose rates ( > 1020 eV • g

-1

s -1

) because of reactions (16), (22) and (22' ). At

high dose rates radical—hydrazine reactions compete less favorably with radical—radical reactions

and N2 H4 is observed in significant yields (71—0216, 69—0272, 68—0101). N2 H4 is also an important

product in flow-systems (see sec. 3.2.6).

Reactions (27) and (29) are likely sources of N2 but their relative importance is uncertain.

Competition between (27) and (28) is an important consideration but contradictory values have

been reported for k^jk^. Volpi and Schiavello (62—0131) have found NH3 and N2 in a 2:1 ratio are

the only products when H atoms from a microwave discharge flow into hydrazine vapor; and have

concluded that &27 ^ &28 - Stief (70-7065) on the other hand has reported &28 = 4A;27 on the basis

of a study of the reaction of H atoms with isotopically labeled hydrazines. There is no apparent

reason for this contradiction.

2.2. Yields of Intermediates

2.2.1. Neutral Species

Yields of intermediates involved in radiolysis of gaseous ammonia are summarized in tables

2.2.1 — 2.2.3. Values cited refer to the total yield of intermediates from both primary and

secondary processes (i . e . , from process 1 and from both primary and secondary reactions of the

ions and excited molecules produced in processes 1 and 2 (table 2.1)). In ammonia, secondary

reactions of ions include rapid ion—molecule reactions with NH3 and subsequent neutralization.

Dissociation (3,4,5) is apparently the only important reaction of excited ammonia molecules. Most

of these yields have been inferred from studies with additives. Although the imaginative use of

additives has been an invaluable source of information about mechanism, the significance of such

information is often compromised by assumptions that must be made about the role of the

additive.

A summary of values of g(H) obtained with a variety of additives is given in table 2.2.2.

Presumably in all cases the additive, AH, reacts with H to produce H2 , AH + H H2 + A.

In most cases, the limiting value of G(H2 ) calculated on the basis of energy absorbed in ammonia

is assumed equal to g(H) + g(H2

). Results are in reasonably good agreement except for those

obtained with propane as additive. Eyre and Smithies (70-0479) have recently shown that G(H2 ) from mixtures of propane and ammonia decreases with dose at doses in excess of about 5 x 1018 eV/g, presumably because of the build-up of propylene. They suggest that the lower values

reported in earlier studies with mixtures of ammonia and propane (68—0659, 69—0326) may be low

for that reason. The value g(H) = 12.5 reported by Jones and Sworski (67—0270) is significantly higher than the

other values in table 2.2.2. Their limiting value of G(H2 ) is in agreement with that reported by

Eyre and Smithies (70—0479) for the NH3 —

2 H4 system; but Jones and Sworski obtain a higher

g(H) because of a relatively large correction for the reactions NH2 + H —

NH3 and N2 H3 + H —

N2 H4

. The magnitude of this correction, which is obtained by a kinetic analysis of G(H2 ), seems

quite large in view of the relatively high rate for H + N2 H4 —> H2 + N2 H3 (table 2.1). In any event,

such a correction should be unnecessary for the other studies in table 2.2.2 except 69—0272 and

70—0216, because of the much lower dose rates involved (for dose rates see tables 3.1.1 and

3.1.2).

If the high value of Jones and Sworski and the low values obtained in the earlier studies with

propane are disregarded, an average value of 10.4 is obtained for g(H), and this is the preferred

value. Table 2.2.2 does not include results obtained with D2 as additive. Jones and Sworski (67—

0270) find g(H) = 12.5 at 200 torr in good agreement with their results from NH3 — N2 H4 ; however,

at 600 torr the analysis leads to g(H) = 90 ± 66. Studies of the NH3 —

2 system by Johnson and

Simic (68-0659) indicate a chain reaction is involved in the formation of HD.

6
Table 2.2.1. Yields of intermediates in radiolysis of gaseous ammonia

Species Yield a (g) Radiation Method of Determination Comments Reference

H 5.1-12.5 — — Preferred value is 10.4. See table 2.2.2 and section

2.2.1. —

NH2 10.4 1.0-1. 7 MeV e“ Anal, of yields from NH3 Calculated on the basis of an assumed mechanism. Pulse

radiolysis, very high dose

rate (10

27 eV-g_l s

_1

).

Boyd.. 71-0216

NH2 8.4 2 MeV e~ g(NH2 ) = g(NH/)/(fraction of NH2 from NH/)

Assume g(NH/) = 100/IF; estimate fraction of NH2 from NH/ by studies of NH3 - SF6

. Pulse radiolysis.

Gordon.. 71-016*

nh2 14 1 MeV e~ Assume g(NH2 ) = 2g(H2 ) +

g(H)

Value probably too high.

Based on the unlikely assumption that reaction (12) is exclusive source of non—radical H2 (see section 2.2.2.) and

g(H) = 12.5 (from NH3 - N2 H4).

Jones. 67—0270

nh2 11.9 -

2-g(NH)

“Co-y Based on material balance: g(NH2 ) + 2g(NH) = g(H) + 2g(H2

).

giH) = 10.

b

; g(H2 ) = 0.75. Assuming g(NH) = g(H2), preferred value is g(NH2 ) = 10.4.

Eyre. 70-0479

NH 0.74 1.0 - 1.7 MeV e

- Anal, of yields from NH3 See comments for NH2

. Preferred value is g(NH) = 0.75 Boyd. .71-0216

NH 0.4 250 keV e~ UV spectroscopy Pulse radiolysis. Yield is low. Used N2 0 as dosimeter

and assumed G(N2 ) = 9.68. Accepted value at dose rate < 10

19 eV-gJ s1 is G(Nj) =

10.0 (66-0434); G(N2 ) is 12.4 at 1027 eV-g-'s'1 (68—0318). Dose rate employed

here was ~ 10

26 eV-g

_1 s

_1

.

Meabum.68—01C

h2 0.7 - 0.8 — — See table 2.2.3. Preferred

value is 0.75. —

nh4 + 3.9 “Co-y Decrease in G(H2 ) when SF6 (0.2%) is added to NH3 + C3 H8 (1.5%).

Agrees well with value calculated from W = 26.5 eV per

ion pair for e

_ —radiation (64—0177) if essentially all positive ions converted to NH/ before neutralization.

Johnson. 68—0659,

67-0369

NH/ 3.5 “Co-y Decrease in G(H2 ) when SF6 is added to NH, — isopropanol

(0.5%).

Eyre. 70-0479

NH/ 3.3 “Co-y Decrease in G(H2 ) when N2 0

is added to NH, — isopropanol

(0.5%).

Eyre. 70-0479

NH/ 4.0 “Co-y Decrease in G(H2 ) when CC14

is added to NH, — isopropanol

(0.5%).

Eyre. 70-0479

a. Unless otherwise indicated yields were measured at ~ 20°C and ~ 1 atm. Yields are in ions, radicals or molecules per 100 eV and refer to the total yield of the intermediate from reaction 1 and from primary and

secondary reactions of the ions and excited states produced in reactions 1 and 2 (table 2.1).

b. Eyre and Smithies (70—0479) distinguish between H atoms produced by ion neutralization and those produced

by other reactions (such as 3 and 5). No such distinction is made in this paper and the value 10.4 refers to the total yield of H atoms (calculated from g(H) and g(e

-

) values reported by Eyre and Smithies).

7
Table 2.2.2. Yield of H-atoms'

Yield(g') Radiation Method Comments Reference

12.5 1 MeV e~ Kinetic anal, of G(H 2 ) from NH3 - N2 H4

. Assume H + N2 H4 —» H2 + N2 H3 ; calculation of g(H) allows for NH2 + H ^ NH3 and H + N2 H3 N2 H4

. b

Jones. 67-0270

10.4 1.0 - 1.7 MeV e~

Kinetic anal, of product yields from

pure NH3

. Pulse radiolysis. Very high dose rate (2= 10

26 eVg_l s

_1

)- Boyd. .71-0168

10.8

60 pLo-y G(H2 ) from NH3 — N2 H4 ; g(H) = G(H 2 ) —

g(H 2 ) - 11.6 - 0.8.

c Assume all H react with N2 H4 to give H2

. Eyre. 70-0479

10.6

60 nCo-y G(H 2 ) from NH3 - N2 H4 As above. Carstensen67—0701

10.4 Sn0 1 Kinetic anal, of G(H2 ) from NH3 -

methanol; g(H) = G(H2 ) - g(H 2 ) = 11 . 2 - 0. 8

.°

Assume H + CH3 OH H2 + CH2

( scavenges all H. )H Eyre. 70-0479

9.5

60 /~* Co-y Kinetic anal, of G(H2 ) from

NH3 — methanol. As above. Carstensen67-0701

10.6 60 Co— n

y

G(H2 ) from NH3 —cyclohexane;

g(H) = G(H2 ) - g(H 2 ) = 11.4 - 0.8.

c

Assume H + C6 H12 —» H2 + C6 H n

scavenges all H.

Eyre. 70-0479

10.6

60 ^Co—

y

G(H2 ) from NH3 -isopropanol;

g(H) = G(H2 ) - g(H2 ) =

11.4 - 0.8.

c

Assume all H react with isopropanol to give H2Eyre. 70-0479

10.0

60 Co—

y

G(H 2 ) from NHj—propane;

g(H) = G(H2 ) - g(H2 ) 10.8 - 0. 8 . c

Assume H + C3 H8 —» H2 + C3 H7 scavenges all H. G(H2 ) decreases with dose above ~ 5 x 10

18 eV/g.

Eyre. 70-0479

7.2

60 s~> Lo—y As immediately above but g(H) =

8.0 - 0 . 8. c Lower value may be result of dose effect (dose not stated). See comment immediately above.

Johnson. 68-0659,

67-0369

5.1

60 Co—

y

As immediately above but g(H) =

5.8 - 0.7.

c See comment immediately above. Nishikawa..69-032(

10.4 1.0 - 1.7 MeV e“

Kinetic anal, of product yields from

pure NH3

. Pulse radiolysis. Very high

dose rate (2s lO^eVg^s-1

).

Boyd. .71-0216

a. Unless otherwise indicated yields were measured at ~ 20°C and ~ 1 atmosphere. Yields are in atoms per 100 eV and refer to the total yield of H from reaction 1 and from primary and secondary reactions of the ions and excited states produced in reactions 1 and 2 (table 2.1).

b. Correction based on kinetic analysis of G(H2 ) data. Correction should be unnecessary for other work in this table except 71-0216.

c. See table 2.2.3.

d. See also 68-0505. These authors have also used C3 H8 to obtain g(H) at high pressure (68—0505, 69-0026).

The limiting value of G(H2 ) for pure ammonia at dose rate less than lO^eV-g^s-1 and at temperatures near 200°C (see section 3.2.3) has also been used to estimate g(H) (67—0270,

68-0659, 70—0479). It is assumed that when the limiting value of G(H2 ) is reached, all H atoms

react with either NH3 or N2 H4 to produce H2

. Depending upon the origin of the yield of nonscavengable H2 , it is assumed that G(H2 ) =g(H) + g(H2 ) or G(H2 ) = g(H) + 2g(H2

). Combination of

the high temperature plateau value of G(H2 ), 15, with a g(H2 ) of 0.8 (table 2.2.3.), leads to g(H) =

13-14, a value significantly higher than has been obtained by any of the scavenger techniques.

However, this estimate involves the important assumption that H2 is not produced by reaction of

N2 H3 or N2 H2

. Eyre and Smithies (70—0479) have suggested that thermal decomposition of N2 H3 and/or N2 H2 may increase with increasing temperature, and thus lead to an increased yield of H2

. They assume that at temperatures near 20°C, N2 H3 and N2 H2 lead to N2 but not to H2 (see table

2 . 1 ).Additives known to act as efficient thermal hydrogen atom scavengers have been used to determine the yield of molecular hydrogen (see table 2.2.3). In general, the limiting yield of

hydrogen in the presence of such scavengers can be used to obtain g(H2 ) if proper allowance is

8
Table 2.2.3. Primary yield of H.

Yield (g) Radiation Method Comments Reference

0.81 “Co-y Limiting value of G(H 2 ) in presence of propylene.

Assume1 H + C3 H6 —» C3 H7 , NH2 + C3 H6 —» C3 H6 NH2

. G(N2 ) reduced from 1.45 to ~ 0.3.

Eyre. 70-0479

0.80 “Co—

y

As above. G(N 2 ) reduced from 1.9 to *£0.3. Johnson. 68-0659

0.70 -

0.82

60 Co—

y

As above. — Nishikawa. .67-0263

0.84 250 keV e~ As above. Pulse radiolysis. Meaburn. 68-0101

1.4 Fast e As above. High value may be result of failure to correct for H2 from

C3 H6.

Sorokin. 65—0523

0.74 1.0 - 1.7 MeV e

Kinetic analysis of product yields

from pure NH3

. Pulse radiolysis. Very highdose rate (*£ lO^eV-g 1 s

_1

)

Boyd. .71-0216

0.75 1 MeV e~ Limiting value of G(H2 ) in presence of ethylene. Acts similarly to propylene.

G(N2 ) reduced from 1.5

to 5* 0 . 6 . c

Jones67-0270

0.74

60 /-> Co—

y

As immediately above. Also used C2 D4

. Nishikawa. 68—0051,

67-0263

0.84

60 Co—

y

Limiting value of G(H 2 ) in presence of benzene. Assume11 H + C6 H6 —> C6 H7

. G(N2 ) reduced from 1.45 to ~ 0.3.

Eyre. 70-0479

1.0

60 Co—

As immediately above. G(N2 ) reduced from 1.4 to 1.0. Aniline not detected. Carstensen67-0701

0.8

60/--' Co—

y

As immediately above. — Johnson. 68—0659

a. Unless otherwise indicated yields were measured at ~ 20°C and ~ one atmosphere. Yields are in molecules

per 100 eV and refer to total yield of H2 from reaction 1 and from primary and secondary reactions of the

ions and excited states produced by reactions 1 and 2 (table 2 . 1). b. Charge exchange between NH3 + and C 3 H6 is energetically possible but should be negligible at concentrations

involved. Proton transfer from NH4 + to C3 H6 ruled out on basis of proton affinities: ~ 9.2 and 6.6 eV for NH3 and C 3 H6 , respectively (62—9017).

c. N2 determined mass spectrometrically. Presence of C2 H4 led to analytical difficulties.

d. Charge exchange between NH3 + and C6 H6 is energetically possible but should be negligible at concentrations

involved. Proton transfer from NH4 +

is probably ruled out on basis of proton affinities: ~ 9.2 and *£ 6.3 eV

(62-9017).

made for energy absorbed in the additive. Results with a variety of additives are in good

agreement and lead to g(H2 ) = 0.75.

Relatively few values of g(NH2 ) have been reported. Gordon, Mulac, and Nangia (71—0169)

estimate g(NH2 ) = 8.4 from g(NH4 +

) and the fraction of NH2 produced by neutralization of NH4 + They assume g(NH4 +

) = 100IW (W is the energy in eV to produce an ion pair) and estimate the

fraction of NH2 produced by neutralization of NH4 + from a comparison of results of irradiation of

pure NH3 and of NH3 in the presence of SF6

. Jones and Sworski (67—0270) have suggested g(NH2 ) = g(H) +2g(H2 ) on the basis of the unlikely assumption that non—radical H2 arises exclusively via

reaction (12). As noted earlier (sec. 2.1.1) studies of mixtures of NH3 and CC14 indicate g(12) — 0.1

(68—0051) whereas g(H2 ) = 0.75. Reaction (4) probably accounts for a significant fraction of non—

scavengable H2. In photochemistry 12 — 14% of the dissociation at 147 and 123.6 nm (64—7003,

62—0132) is attributed to (4),

(4) NH3 * -> NH + H2 and NH has been observed spectroscopically by Meaburn and Gordon (68—0101) in pulse radiolysis

of NH3. Meaburn and Gordon estimate g(NH) — 0.4, but this is probably low because of an error

in dosimetry (table 2.2.1). On the basis of material balance one expects g(NH2 ) =g(H) + 2g(R2 ) —

2g(NH). The best assumption seems to be that g(NH) = g(H2 ) and this leads to a preferred value

of 10.4 for g(NH2

). 9
More recently Boyd, Willis, and Miller (71—0216) have shown that their product yields from

radiolysis of pure ammonia with single pulses of electrons (1.0 — 1.7 MeV) at very high dose rate

(2* lO^eV-g^s'1 ) are constant with g(H) = g(NH2 ) =10.4 and g(H2 ) = g(NH) = 0.74. At the high

dose rates employed, radical—product reactions are not significant and they assume the following

mechanism:

(13) NH2 + H ^ NH3 (13') NH2 + H —» NH + H2 (14) NH2 + NH2 N2 H4 (15) NH2 + NH2 -» NH + NH3 (18) NH + NH —» N2 H2 * N2 + H2 (24) H + H -* H2 They take kl4 + kls = 2.3 x 109 dm3 molds'1 and calculate, using a computer program based on

that of Schmidt (66-8024), G(N2 H4 ), G(H2 ) and G(N2 ) for various values of kxJkX3 and kx3 , kxy , kXB and k2A . G(N2 H4 ) depends mainly upon kX3 and ku and G(H2 ) depends primarily upon kn , for fixed

values of kn and &14 . Agreement between calculated and observed product yields is achieved for very reasonable

values of the various specific rates (kX3 = 1.8 x 1010

, kxy = 2.9 x 109, kH = 1.8 x 109, 115 = 5 x 10®,

kXB =5 x 10 10 and kM = 1.6 x 10® dm3 mol-1 s'

1 ). These results represent a re-examination and

extension of an earlier study (69-0272).

2.2.2. Yields of Ionic Species

Johnson and Simic (68—0659, 67—0369) have determined g(NH4 +

) from the reduction by SF6 of

G(H2 ) from mixtures of NH3 and propane. G(H2 ) is 8.0 for NH3 containing 1.5 mole percent

propane. Addition of 0.2 mole percent SF6 reduces G(H2 ) to 4.1. SF6 reacts rapidly with thermal

electrons (66—9159) but only very slowly with hydrogen atoms and free radicals generally (67—

0093, 66—0249, 64—9016). Therefore, the observed reduction in G(H2 ) is attributed to modification

of the neutralization process. In NH3 —C3 H8 , neutralization of NH4 +

is assumed to proceed via (11)

and (12) whereas in the presence of SF6 , NH4 +is neutralized by SF6 '. This latter process is assumed not to produce H or H2 and hence AG(H2 ) = g(NH4 +

). The value obtained, 3.9, agrees

well with g(NH4 +

) calculated from W =26.5 eV per ion pair (64—0177) assuming essentially ail positive ions are converted to NH4 + before neutralization.

Nishikawa, Kuroda, and Matsuura (69—0326) also have studied the NH3 —

C

3 H8 —SF6 system; but

while results are qualitatively similar, they find the decrease in G(H2 ), AG(H2 ) is only about 2. Their value of G(H2 ) for the ternary system is about the same, 3.8, as that reported by Johnson

and Simic but G(H2 ) for NH3 —

C

3 H8 is significantly lower.

Johnson and Simic (68—0659) have investigated the system NH3 —

C

3 H8 -N2 0 which might be

expected to be similar to the NH3 -C3 H8 —SF6 system since both Nz O and SF6 are good electron

scavengers and poor H—atom scavengers. Although addition of N2 0 to mixtures of NH3 and C3 H8 does reduce G(H2 ), the decrease, 3.0, is less than that produced by addition of SF6 , 3.9.

Nishikawa, Kuroda, and Matsuura (69—0326) have also studied this system and report similar

results.

More recently Eyre and Smithies (70—0479) have carried out similar studies on mixtures of

ammonia and isopropanol (0.5%). G(H2 ) is 11.4 for this system and introduction of SF6 , N2 0 or CC14 reduces G(H2 ) to limiting values which are respectively 7.9, 8.1 and 7.4. They conclude that

AG(H2 ) = g(NH4 +

). Using the weighted mean of AG(H2 ) they obtain g(NH4 +

) = 3.4. Presumably, the

yield of H from sources other than ion—neutralization is then 7.0.

3. Product Yields

H2 , N2 and N2 H4 are the products observed in radiolysis of gaseous ammonia but yields depend

upon a number of parameters such as temperature, pressure and dose rate. Yields at 10
approximately 20°C and one atmosphere pressure are summarized in section 3.1, and the

influence of various parameters is discussed in 3.2.

3.1. Product Yields for Radiolysis Under

Static Conditions at ~ 20° C and ~ 1 Atmosphere

H2 and N2 are the only measurable products at dose rates up to at least 2 x 1018 eV-g-1 s

_1 (table

3.1.1); G(H2 ) = 5.0 ± 1.0 and G(N2 ) =1.7 ± 0.3. Presumably, the steady—state concentration of

hydrazine is kept very low because of radical—hydrazine reactions (see sec. 2.1.2).

At very high dose rates (2= lO^eV-g^s-1

) hydrazine is produced in significant yield in static

systems (71-0216, 69—0272) because radical—product reactions do not compete effectively with

radical—radical reactions. Hydrazine is also a product in flow systems (see sec. 3.2.6).

In all cases the total dose was sufficiently low to preclude variations in product yields

associated with high conversion (see sec. 3.2.1). Indeed, the only obvious variables are dose rate and the LET (linear energy transfer), of the radiation. Both of these factors may contribute to the

relatively large scatter in yields but it is clear from table 3.1.2 that they alone are not responsible.

Other probable contributing factors include the presence of trace impurities and problems in

dosimetry. The neutralization process in particular should be quite sensitive to trace impurities,

the presence of which would probably lead to low yields (see sec. 2.1.1). Most of the results

summarized in this sec. are based on dosimetry with nitrous oxide. Problems associated with gas

phase dosimetry in general (71—0062, 67—0546, 71—0179) and the nitrous oxide dosimeter in

particluar (71—0062, 68—0318, 67-0027, 66—0434, 61—0103) have been discussed elsewhere.

Table 3.1.1. Product yields from radiolysis of gaseous ammonia with various radiations under static conditions at ~ 2(PC and ~ 1 atm*

Radiation G(-NH3 ) G(H2 ) G(N2 ) G(N2 H4 ) Dose Rate

(eV - g

_1

s

_I

) Comments Reference

1 MeV e

_ 3.0 4.5 1.5 0.0 2 x 10 18 b Yields depend upon dose

rate. See section 3.2.2

Jones. 67-0270

1.0 - 1.7 MeV e~ — 3.6 1.0 0.58' 2 x 10

26 and

2 x 10

27 d Pulse radiolysis. Boyd.. 71—0216 and

Willis.. 69-0272 ~ 250 keV e“ — 2.3' 0.68' 0.07' ~ 10* (4.0 x 10“

eV/pulse).' Pulse radiolysis. Meabum.68-0101

“Co-y 2.7 -

4.7

4.1 -

7.0

1.4 -

2.3

0.0 - 0.001 — See table 3.1.2. —

*H+

(0.8 MeV) 4.0 6.0 2.0 0.0 = 3 x 10

15 1 Yields depend on dose

rate. See section 3.2.2 Horscroft64—0174

2 H

+

(2 MeV) — — — 0.5 not reported No attempt to measure G(H2 ) or G(N2

).

Lampe... 63-0098

4 He2+ 3.0 -

4.2* — — — — See table 3.1.3. —

Reactor

(y + n)

3.8 5.7 1.9 “ Dolle58-0051

a. For yields at other temperatures and pressures see section 3.2.

b. NjO dosimetry; G(N2 ) = 10.0 (66—0434).

c. N2 H4 is a significant product in static system only when dose rate is high enough to reduce the importance of radical—

2 H4 reactions.

d. N2 0 dosimetry; G(N 2 ) = 12.4. Value obtained by adiabatic calorimetry (68—0318). Probably applies only to very high dose rates.

e. These values are probably low because they are based upon N2 0 dosimetry with G(N2 ) = 9.68. Generally

accepted value is G(N2 ) =10 for dose rates less than about 10

19 eV-g

_1 s ~l

. Value may be higher at higher dose rates (see d above). The dose rate is estimated from the dose per pulse on the basis of a cell volume

of 0.68 liters and a pulse duration of ~ 40 ns.

f. Dosimetry based on charge collection; value in eV g

_1 s_1 involves estimate of effective volume. This is lowest dose rate employed.

g. Most yields originally reported as molecules per ion pair (M/N); these have been converted to G assuming W

= 30.5 eV per ion pair in NH3 for *He2+ radiation (53—0008).

11
Jungers (36—0001) has studied the relative rates of decomposition of NH3 and ND3 by 4 He2+ radiation at 525 torr. At 20°C, the ratio G(—NH3): G(—ND3) is 1.27. Absolute yields were not reported.

Table 3.1.2. Product yields for gamma radiolysis at ~ 20°C and ~ 1 atm*

G(-NH3 ) G(H2 ) G(N2 ) G(N 2 H4 ) Dose Rate

(eV-g

_1 s_1

)

Dosimetry Reference

4.7 7.0 2.3 0.0005 -

0.001

1.5 x 10 16 Not stated. Sorokin. 64— 1757

4.2 (4.0)

b 6.3 (6.0)

b — — 7.0 x 10 15 N2 0; G(N2 ) = 10.6. Anderson. 67-0546

4.0 6.0 2.0 0.0 6.0 x 10

16 N2 0; G(N2 ) = 10.0. Kazanjian. 68-0555

3.8 5.7 1.9 0.0 1.4 x 10

16 N2 0; G(N2 ) = 10.0. Johnson. 68-0659c

(3-3) (4.9) (1-6) — (5 x 10 14

) Fricke. d DoUe58-0051

3.0 4.5 1.5 — 6.9 x 10

15 C2 H4 ; G(H2 ) = 1.2. Buchanan. 70-0134

2.9 4.3 1.4 0.0 2 x 10

15 N2 0; G(N2 ) + G(02 ) = 12.0. Nishikawa. 68—0051

2.7 4.1 1.4 0.0 5 x 10

14 Nz O; G(N2 ) = 10.0. Carstensen67-0701

2.7 4.1 — — Not given. — Nishikawa. .68-0505

2.7 4.1 1.4 — 9 x 10 14 N2 0; G(N2 ) = 10.0. Nishikawa. .69—0326

2.9 4.4 1.4 SS 0.005 3 x 10

15 N2 0; G(N2 ) = 10.0. Eyre. 70-0479

a. Results from 63—0165 excluded as unreliable.

b. Corrected on the basis that G(N2 ) = 10.0 rather than 10.6 (66-0434).

c. See also 67—0369.

d. Without wall corrections; values are of questionable validity.

Table 3.1.3. Yields for radiolysis with alpha particles at ~ 2(PC and ~ 1 atm *

Source G(-NH3 ) G(H2 ) G(N2 ) Dose Rate

(eV-g

_1 s_1

) b Comments Reference

Rn 3.0

C 4.5

C 1.5C Used 4 He2+ sources of comparable strength

to those used by Luyckx

(34-0003).

Wourtzel 19-0001

Rn 3.8 See immediately above. Yield depends upon dose rate; value given obtained by extrapolation

to zero dose rate.

Jungers32—0002

Rn 4.2 ~ (0.1 — 5) x

10

16 Yield depends upon dose rate; value given obtained by

extrapolation to zero dose

rate.

Luyckx34—0003

Ra 3.6 — — ~ 5 x 10

13 — Essex. 34—0001 Ra 3.6 — — ~ 6 x 10

14 — Burtt.57—0018

210 Po 3.5 5.2 1.7 7.6 x 1017 — Kazanjian. 68-0555

a. In all studies except 68-0555, yields were originally reported as molecules per ion pair ( M/N). These have

been converted to G assuming W = 30.5 eV per ion pair for

4 He2+ radiation (53-0008).

b. In all studies except 68-0555 dose rates were not reported as such. Values were calculated from data given. In 68-0555 N2 0 was used as dosimeter and G(N2 ) was assumed to be the same as for MCoy

(10.0). Recent work of Sears (69—0085) supports this assumption. Dose rates for other studies have been estimated from

original data and W = 30.5 eV per ion pair.

c. Original data leads to G(-NH3 ) = 2.6. Values cited here are based on recalculations by Jungers (32-0002).

12
3.2. Effect of Various Parameters

3.2.1. Dose

At dose rates such that H2 and N2 are the only products, G(H2 ) and G(

2 ) are independent of

total dose up to at least 8 x lO^eV/g (table 3.2.1). At very high conversions, yields should decrease

because of NH2 + H2 —> NH3 + H (64—0174, 32—0002). The inhibiting effect of H2 has been

observed in photochemical studies of NH3 (55—7001, 44—7000).

At dose rates of the order of 1026 eV*g-1 s

_1

, N2 H4 is a product and because N2 H4 reacts with H

and NH2 , product yields may be independent of dose over a more limited range. Available data

indicate independence of dose extends at least up to 6 x 1020 eV/g (at lO^eV-g^s'1 ) (69—0272). At

these high dose rates the total dose is delivered as a series of pulses of very short duration (50—

100 ns).

Table 3.2.1. Effect of dose

Radiation Effect of G(-NH3 )‘ Max. Dose (eV/g) Reference

Fast e~ none 8 x 10

22 b Sorokin. 65—0523

Fast e~ (1 MeV) none 4.5 x 1021 Jones. 67-0270'

60 nLo-y none 3 x 10

22 Kazanjian.68-0555d

4 He2+

( 210 Po) none 6 x 10

22 Kazanjian. 68—0555

'fTfO.S MeV) none 6 x 10

21 eV totally absorbed in 0.5 cm

3

. Horscroft64—0174

a. At dose rates employed N2 and H2 were the only products observed. Relevant dose rates can be found in tables 3.1.1 and 3.1.2.

b. Corresponds to about 5% conversion.

c. See also 69—0272 for results with fast e at very high dose rate (10

2

‘ eV g

_1 s_1

). d. See also 58-0051, 64-1757, 67-0701, 70-0134.

3.2.2. Dose Rate

At pressures near one atmosphere G(—NH3 ) decreases with increasing dose rate (table 3.2.2)

and the magnitude of the effect decreases with decreasing pressure (67—0271, 34—0003).

Sorokin and Pshezhetskii (65-0523) report G(—NH3 ) independent of intensity; however, their

investigation was limited to a relatively small (eight—fold) variation in dose rate. The results of

Jones, Sworski and Williams (67—0271) obtained under similar conditions, but for a much wider

(100—fold) variation in dose rate, indicate that G(—NH3 ) should change only by about 10% over the

range employed by Sorokin and Pshezhetskii.

Burtt and Baurer (55—0010) and Burtt and Zahlen (57—0018) have reported G(—NH3 ) increases

with increasing intensity at 200 torr but the intensities were much lower than are usually

encountered (table 3.2.2).

The observed decrease in G(—NH3 ) with increasing dose rate has not been satisfactorily

explained. No effect is expected on the basis of the simple mechanism discussed in sections 2.1.1

and 2.1.2. That mechanism assumes that ions and excited neutrals produced in the early stages of

radiolyisis undergo reactions that lead principally to NH2 , H, NH, and H2

. The radicals in turn

react with each other and with other intermediates such as N2 H4 and N2 H3 to give the observed

products.

If reaction (23) is included in the mechanism, G(—NH3 ) would

(23) H + NH3 —> H2 + NH2 be expected to decrease with increasing intensity. The specific rate of (23) has not been accurately

measured but estimates of 5 dm3 mol-1 s

-1 (65—0555) and 200 dm3 mol_1 s

_1 (69—0272) have been

reported for temperatures near 20°C. If is in fact as high as 200 dm3 mol-1 s

-1

, reaction (23)

13
Table 3.2.2. Effect of dose rates at ~ 23°C

Radiation* Dose Rate (eV.cra

-3 s-1

) Effect on G(-NHj) Reference

1 MeV e* 6.5 -> 650 x 10 14 fc Decreases from 3.5 to 2.6 at 700 torr; negligible effect at 200 torr.

Jones.. 67—0271

Fast e“

* 8 -» 60 x 10

14 None. Sorokin .65—0523

4.0 x 1014 -> 9.8 x 10 w 4 Decreases from 4.0 to 1.6 at 300 torr (only

P studied). G appears to be leveling off

at ~ 1.6.

Horscroft64—0174

4He,+ 10“ 5 x 10 13 Decreases 30% at 450 — 700 torr; effect diminishes below 450 and is negligible below ~ 140 torr.

Luyckx34-0003e

4He** 1.7 - 30 x 10

10 Increases from 2.4 to 3.4 at 200 torr. Burtt. 55-0010,

57-0018

a. No results from a single laboratory for “Co-y radiation.

b. Originally reported in eV/min. Cell volume was ~ 26 cm3

. c. Energy not specified; very limited dose rate range.

d. Originally reported in eV/s absorbed in a total volume of 0.5 cm3. e. See also 32-0002.

should compete at the dose rates employed and thus could account for the observed dose rate dependence.

At very high dose rates (5= lO^eV-g^s-1

), the system is somewhat simpler because radicalproduct reactions are not significant. At 20°C, yields are unchanged when the dose rate is increased from 2 x lQ^eV-g^s*1 to 2 x HPeV-g^s-1 (1.0 — 1.7 MeV e~; 71—0216). However, at higher temperatures yields of H2 and N2 H4 are lower at the higher dose rate and the effect

increases with increasing temperature (see fig. 3.2.3. 1). G(N2 ) remains insensitive to changes in

dose rate up to the highest temperature studied, 460°C. At 20° reaction (23) probably does not

compete effectively with radical—radical reactions at these high dose rates and thus dose rate

effects would be expected to be negligible. At higher temperatures, reaction (23) will compete more

favorably.

3.2.3. Temperature

At dose rates less than about 2 x 1018 eV-g-1 s

_1 G(—NH3 ) increases markedly with increasing

temperature and appears to reach a plateau value, of about 10 near 200°C. Although there is agreement on the plateau value, there is significant variation in data at intermediate temperatures

(see fig. 3.2. 3.1) which may result at least in part from differences in dose rate and pressure. At

all temperatures H2 and N2 are the only products.

A number of interpretations of the effect of temperature have been proposed. Anderson and

Winter (67-0546) attributed the increase in G{—NH3 ) with increasing temperature to changes in

solvation of NH4

+ and the influence of solvation upon ion—neutralization. At high temperature

NH4 +

is presumed to be unsolvated and the pertinent reactions are NH4 + + e~ -> NH3 * + H

NH3 * -* NH2 + H.

At low temperatures NH4 +

is fully solvated and the neutralization reaction is more appropriately

written

NH4 + (NH3 ) n + e- (NH3 )*b+1 + H.

The excess energy associated with the excited NH3 complex is about 80 kcal less than that for

NH3 * produced by neutralization of unsolvated NH4 + and as a consequence, further dissociation to NH2 and H is not energetically possible.

14
Figure 3.2.3. 1. Variations ofG(—NH3 ) with temperature at dose rates less than 1019eFg-1

s -1

. Original data in terms of G(H2 ); G(-NH3)=2/3 GH2 ). O 67-0546 (7.0 x KPeV g^s-1

); • 67-0270 (2.0 x 1018 eV-g_1 s1 ); A 68-0659 (1.4 x lO^eV-g-^-1 ); 70-0479 (3 x lO^eV-g^s'1 ).

Solvation of NH4 + in gaseous ammonia is known to occur (68—0032, 66—9067, 64-9015) and

modification of ion—neutralization in the manner suggested is not unreasonable. However,

considerably higher temperatures than these are required to produce the necessary changes in

solvation (68—0032, 66—9067). For example at 100°C and 1 torr n = 2 and neutralization to give more than one H is still endothermic (69—0326, 66—9067). Also, Johnson and Simic (68—0659) have

found G(H2 ) from mixtures of ammonia and propane and depression of G(H2 ) from such mixtures

by SF6 are independent of temperature, and they conclude that the hydrogen yield from

neutralization of NH4 + by e

-

is independent of temperature.

Jones and Sworski (67—0270) have interpreted the effect of temperature in terms of competition

between reactions (13), (22), (23) and (24).

(13) H + NH2 + M —> NH3 + M

(22) H + N2 H4 ->H2 + N2 H3 (23) H + NH3 —> H2 + NH2 (24) H + H + M^H2 + M

They assume that reaction (23), which has an energy of activation of 10—15 kcal/mol (62—0131) is unimportant at room temperature but becomes significant at higher temperatures. Johnson and

Simic (68-0659) reject this interpretation on the basis that the energy of activation for reaction

(23) is too high to account for their observed temperature dependence. They suggest that increase

in G(-NH3 ) with temperature is best explained in terms of competition between reactions (13) and

(22). An Arrhenius plot of their data leads to an apparent energy of activation of about 2.1

kcal/mol. (A similar treatment of the data of Jones and Sworski (67—0270) leads to a value of 1.7.) In terms of their mechanism this apparent energy of activation is to be identified with the

differences in activation energies of reactions (22) and (13). Reaction (22) has been reported to have an activation energy of 2.0 kcal/mol (62—0131) while (13) would be expected to have an

activation energy near zero. Thus, the observed temperature dependence agrees well with their

mechanism. An important implication of this mechanism is that reaction (23) is unimportant at least up to 200°C. However available specific rate data indicates that reaction (23) should compete

favorably with reaction (22) at temperatures at least as low as 150°C. For example if the

reasonable assumption is made that the concentration of NH3 is at least 103 times greater than the

steady state concentration of N2 H4 , reaction (23) is about four times faster than reaction (22) at 150°C (specific rates from 62—0131; see also table 2.1).

15
The temperature dependence of G(—NH3 ) at very high dose rates (~ 1027 eV-g-1 s

_1

; 69—0272,

71—0216) differs significantly from that described above (see figure 3. 2. 3. 2). G(—NH3 ) is constant

up to 200°C for a dose rate of 2 x 1027 eVg_1 s

_1

; above 200°C it increases and does not appear to be

leveling off at the highest temperature studied (450°C). At 2 x 1026 eV g

_1 s

_1 the effect is qualitatively similar but G(-NH3 ) is constant only up to about 125°C. Reaction (22) should be

unimportant at the high dose rate employed, and hence interpretation based upon competition

between reactions (13) and (22) can be ruled out. At very high dose rates the effect of temperature

appears to be the result of the increasing importance of reaction (23) at higher temperatures.

Kinetic analysis of the observed temperature dependence for a dose rate of 2 x 1027 eV g

_1 s_1 leads

to &23 = 3.6 x 109 exp (— 10,500/RT) dm3 mol-1 s

-1

. The energy of activation is in agreement with

reported values of 10—15 kcal/mol (62—0131, 65—0555). However, a similar analysis of data for a dose rate of 2 x 1026 eV g

-1 s_1 leads to — 8 x 107 exp (— 7,200/RT) dm3 mol-1 s-1

. Boyd, Willis and

Miller (71—0216) attribute this inconsistency in to variations with temperature of the various

rate constants required in their calculations of k23 . Studies with 4 He2+ radiation lead to results which are at least qualitatively similar. Thus,

Jungers (36—0001) reports an increase in G(—NH3 ) by a factor of 1.9 (absolute yields not reported),

and Wourtzel (19—0001) reports the following values: £(°C), G(—NH3 ); 18, 2.8; 108, 5.6; 220, 8.3;

315, 9.0. The values of Jungers and Wourtzel were originally reported as M/N and have been

converted to G assuming W = 30.5 eV per ion pair for 4 He2+ radiation (53—0008).

Eyre and Smithies (70—0479) have suggested that part of the observed increase in G(—NH3 ) with increasing temperature may be the result of increased thermal decomposition of N2 H3 and/or

N2 H2 ; and they use such an argument to account for the observed discrepancy between g(H)

calculated from the limiting values of G(H2 ) at high temperatures and g(H) obtained by scavenger

methods (see sec. 2.2.1).

Finally, it should be noted that <!>(— NH3 ) for photolysis of gaseous ammonia also increases with

temperature over this same range (32—7001, 34—7003, 44—7000), but results are limited and in

poor quantitative agreement.

Figure 3. 2. 3. 2. Yields of H2 , N2H4 and N2 from radiolysis of NH2 vs. temperature ( 71-0216 , 69—0272 )

OG(Hg), G(N2 H4 ), and AG(N2 )at 2 xlO^eV-g^s-1

; •G(H2 ), G(N2H4)»and AC(N2 ) at 2 x 1027eV- r’s-1

. 3.2.4. Pressure

One atmosphere and below: In a number of the studies summarized in table 3.2.4 G(—NH3 ) has

been reported to increase with decreasing pressure at pressures below one atmosphere.

Jones, Sworski, and Williams (67—0271) using 1 MeV electrons and Carstensen (67—0701) using

“Co-y radiation found G(—NH3 ) independent of pressure down to 400 torr. Below 400 torr 16
Table 3.2.4. Effect of pressures'

Radiation Pressure Range Effect on G(—NH3 ) Reference

1 MeV e” 47 —» 800 torr See fig. 3.2.4 for results at 23°C; At 200°C,

G(—NH3 ) is independent of P.

Jones. .67-0271

Fast e

_ b 50 500 torr (20°C) Decreases with increasing P\ appears to approach

limit at ~ 500 torr. G not given. Sorokin. 65—0523 “Co-y 200 650 ton- (23°C) See fig. 3.2.4. Carstensen67—0701 “Co-y 100 760 torr (23°C) None. Buchanan. 70—0134

60/-Lo—y 400 torr 3.2 atm (41°C) None. Johnson. 68—0659 M Co-y 100 -» 700 torr (20°C) None. Eyre. 70-0479

Tl + 200 600 torr (22°C) Decrease linearly with increasing P, from 1.93

to 1.73. Horscroft64—0174

4 He2+ 80 700 torr (20°C) Decrease with increasing P; total decrease

of 23%. c Luyckx34—0003 d

60 a-Lo—y 1 12 atm (20°C) None. Nishikawa.68—0051

60 a—Lo—y 1 —* 60 atm (120°C) P(atm), G(—NH3 ); 1, 10; 7.7, 15; 9, 14.8; 30,

9.0; 60, 6.6. Sorokin. 64- 1757

60 a-Lo—y 1 atm 0.312 g/cm3 (137°C) Sharp decrease from 4.1 to 1.4 at density near

0.15 g/cm 3

.

Toi.. 62-0074'

a. In all cases incident intensity was constant and therefore variation in pressure is accompanied by a variation

in energy absorbed per unit volume per unit time.

b. Energy' not specified.

c. Author attributes important but unspecified part of this decrease to changes in absorbed intensity. See a above.

d. See also 57-0018.

e. See also 69—0026.

G{—NH3 ) increases from about 2.9 to a maximun of about 4 at 100 torr. Buchanan and Hanrahan

(70—0134) failed to observe a similar increase in their study of “Co—-y radiolysis of NH3

. They

found G(—NH3 ) independent of pressure from one atmosphere to 100 torr, the lowest pressure

studied. Eyre and Smithies (70—0479) also found G(—NH3 ) independent of pressure over this same

pressure range.

Luyckx (34—0003) observed an increase in G(—NH3 ) of about 23% for a decrease in pressure

from 700 to 80 torr in a study of 4 He2+ radiolysis of ammonia. He attributed an important, albeit

unspecified, part of this decrease to the accompanying variations in intensity. Under conditions of

constant incident intensity a decrease in pressure is accompanied by a decrease in the energy

absorbed per unit volume per unit time. All of the studies summarized in table 3.2.4 wr ere carried

out under such conditions; however, the decrease in intensity associated with a change in

pressure from one atmosphere to about 100 torr should not affect G(—NH3 ) by more than about

10% (see sec. 3.2.2).

Burtt and Zahlan (57—0018) tried to determine the effect of pressure in the range 700 — 70 ton- under conditions of nearly constant intensity using 4 He2+ radiation. They conclude that G(—NH3 ) increases with decreasing pressure but the experimental data are limited and not especially

convincing.

Horscroft (64—0174) has reported an essentially linear increase in G(—NH3 ) of about 10%

between 600 and 200 torr in radiolysis with 0.8 MeV protons. At the dose rate employed, intensity

effects should be very small (section 3.2.2.) and the 10% increase in G(—NH3 ) can probably be

attributed solely to the decrease in pressure.

Luyckx (34—0003) has pointed out that his results suggest the existence of an inversion

intensity." Near this "inversion intensity", G(—NH3 ) is relatively insensitive to changes in pressure.

At higher intensities G(—NH3 ) decreases with increasing pressure and at lower intensities it increases with increasing pressure. The inversion intensity arises because G(—NH3 ) is independent

of intensity at pressures below about 140 torr but decreases with increasing intensity at higher

pressures. This may account for some of the discrepancies that have been observed.

17
G(—NH3 ) might be expected to vary with pressure because of the pressure dependence of

radical combination reactions. Combination of two NH2 radicals is apparently pseudo—secondorder at pressures in excess of about 0.45 ton- (63—9010); however, combination of NH2 with H

and of H with H should remain third order up to significantly higher pressures. Jones, Sworski

and Williams (67—0271) attribute their observed increase in G(—NH3 ) between 450 and 100 torr to the decreased importance of combination of NH2 with H. A similar explanation has been offered

to account for increases in 4>(—NH3 ) with decreasing pressure in photolysis of ammonia (54—7002,

39—7001, 35—7002); however, the decrease in <I>(— NH3 ) begins at lower pressure (~ 100 torr).

The rapid and irreproducible decrease in G(—NH3 ) at pressures below 100 torr reported by

Jones and Sworski (67—0270) and by Carstensen (67—0701) is similar to the effect observed by

Wiig (37—7002, 35—7002) in photolysis of ammonia. Wiig attributed this decrease to combination

of NH2 with H at the walls.

NH 3 Pressure , torr

Figure 3.2.4. Variation of G(H2 ) and G(— NH3) with pressure 23°C. AG(— NH3), OG(H2 ), 67-0270

(2 x 1018 eV-g~1 s

_1

); AG(-NHa), #G(H2 ), 67-0701 (5 x lO^eV-g^s"1 ).

At very high dose rate (2 x 1027 eV-g_1 s

_1

), G(—NH3 ) increases rapidly with decreasing pressure

below about 700 torr (69—0272, 71—0216), but this effect appears to be the result of acceleration of

secondary electrons in transient fields created by the pulse.

Pressure above one atmosphere: At higher temperatures, the pressure range can be extended

to the point that gas densities approach those of liquid ammonia. Toi, Peterson and Burton (62—

0074) studied 60 Co—y radiolysis of gaseous ammonia at 137°C over the density range from 5 x

10~4 g/cm3 to 0.312 g/cm3

. They found G(—NH3 ) decreased rather sharply from 4.1 to 1.4 at densities near 0.15 g/cm3

. Further increase in density had little effect upon G(—NH3

). They

interpreted this decrease in terms of the effect of ion-clustering upon ion—neutralization.

However, this interpretation seems improbable in light of more recent investigation of ionclustering in ammonia (64—9015, 66—9067, 68—0032). Recent work by Nishikawa, Kuroda, and

Matsuura (69-0026) over this same density range is in good agreement with the earlier study of

Toi et al. They suggest the decrease in G(—NH3 ) is the result of neutralization of NH4 + by NH2 ~,

i.e.,

NH4 + + NH2 - -» 2NH3 rather than by an electron. They speculate that at high densities NH2 may compete successfully

with NH4 + for electrons because of unspecified alteration in the electrostatic field of NH4

. 18
3.2.5. Electric Field

Electric fields have been applied to systems during radiolysis to obtain information about the

role of ion-neutralization processes (for a general discussion of this technique see G.G. Meisels,

68-0650, page 364). In the case of ammonia, electric fields less than about 5 V-cm'1 torr

-1 do not

significantly affect G(-NH3

). The earliest investigations (38—0002, 42—0001, 55—0010, 57—0018) were carried out with

relatively low—intensity (1013 — 10 14 eV-g-1 s

-1

) 4 He2+ radiation over a pressure range of 200 to 620

torr at 25°C. In the first of these (38-0002), a significant decrease (~ 30%) in G(-NH3 ) with

increasing field strength was reported at 620 torr, and on the basis of this observed decrease it was concluded that 34% of the overall reaction was attributable to ion—recombination. However,

this decrease was not observed in subsequent studies under similar conditions in the same

laboratory using more highly purified ammonia (55—0010, 57—0018).

More recently, Jones and Sworski (67—0270) carried out a study of the effect of applied field

upon radiolysis with 1 MeV electrons. At 200 torr and 23°C they find G(—NH3 ) is independent of

field strength up to about 5 V-cm-1 torr

-1

; G{—NH3 ) increases with increasing field strength above

5 V-cm-1 torr

-1 because of excitation of NH3 by collision with electrons accelerated in the field. These results suggest that the net chemical effect of ion—neutralization is the same whether the

neutralization occurs homogeneously or at a surface.

3.2.6. Flow Rate

Most studies of gaseous ammonia have been made under static conditions. In such cases, hydrazine is not obtained in measurable yields at dose rates below ~ lO^eV-g^s-1 (69—0272, 68—

0101) presumably because of radical—hydrazine reactions. Jones, Sworski and Williams (67—0271)

have studied radiolysis of NH3 in this low dose rate range with 1 MeV electrons under both static

and flow conditions. Hydrazine is not produced in measurable yields under static conditions but it is an important product in flow systems. Yields of N2 H4 increase with increasing flow rate and

decreasing intensity. At constant flow rate and intensity, G(N2 H4 ) increases markedly with

increasing temperature. At a constant beam current of 5 /xA and constant flow rate of 2.5

dm3 /min, increases from 0.62 to 2.97 as the temperature is increased from 25°C to 300°C.

The highest yield observed was G(N2 H4 ) = 3.95 for a beam current of 0.05 /jlA and a flow rate of

2.5 dm3 /min at 300°C.

In flow systems hydrazine is removed from the reaction zone and rapidly diluted so that

radical—hydrazine reactions are considerably less important than in static systems. Increasing

temperature and decreasing intensity further reduce the probability of such N2 H4~consuming

reactions. An increase in temperature is assumed to increase the importance of reaction (23)

relative to the reaction of H with N2 H4 , and decrease

(23) H + NH3 H2 + NH2

in intensity probably favors production of N2 H4 by reducing the steady—state concentration of H.

19
Appendix 1. Selected Properties of Species Involved in

Radiolysis of Gaseous Ammonia

See tables A. 1.1 and A. 1,2.

Table A. 1.1. Properties of neutral species'

Species A//,°(298 K)

(kcal/mol)

I.P. (eV) P.A.

(eV) E.A.

(eV)

£>(298 K)

(kcal/mol)

Other properties

nh3 -11.02 10.2 9.2-9.4b c D(NH2 -H) = 104 ± 2 W = 30.5 ± 0.4 ( 210 Po-a), h 26.5 ± 0.4 (1 MeV e

-

).

1 S A = 0.719j

. UV spectrum.

k

e impact spectrum.

1 nh2 41 11.4 — 1.21,1.22

d D(NH-H) = 90 ± 2 UV spectrum.

m Fluorescence

spectrum". ESR spectrum. 0 NH 79 13.1 — — D(N-H) = 85 ± 2 UV spectrum. p Fluorescence

spectrum. q N2 H4 (g) 22.80 8.74 ' •' - ** D(H2 N-NH2 ) = 59 ± 3 £>(N 2 H3 -H) = 76 ± 2

5 n2 h3 ~ 47* 7.88 — — — —

N,H, 49 ± 5

f 9.85 — — D(HN=NH) = 109 ± 5* —

H 52.10 13.6 — — — —

h2 0 15.4 3.0 -0.72 D(H-H) = 104.2 —

n2 0 15.6 — — D(N-N) = 225.96 —

a. Unless otherwise indicated values have been taken from the following sources. Standard heats of formation

(AH°{ ), Wagman 68—9060; Ionization potentials ( I.P . ), Franklin 69—9067; proton affinities (P.A .) and

electron affinities (E.A.), Vedeneyev 62—9017; bond dissociation energies (D), Darwent 70-9007.

b. See also 55-9002 and 68—7069. Entropy of protonation is —27.55 eV/deg (55-9002).

c. Doesn't form a stable negative ion with thermal electrons. At ~ 3 eV NH” is detected (34-9002). See also 66-0298.

d. Page 73, 62-9019.

e. Calculated from D(N2 H3 — H) and AHf ° of H and N2 H4.

f. Calculated by combining mass spectrometric and thermal data (Foner and Hudson 58-9004).

g. Calculated from AHf ° of N 2 H2 and NH.

h. Biber.. 53-0008.

i. Meisels 64-0177.

j. Stopping power relative to air, Meisels 64-0177.

k. 105—165 nm with 0.7 nm resolution, Okabe and Lenzi67—7484 (includes threshold for various photodissociation processes); 140—220 nm, Watanabe 54—9006; 85—230 nm, Duncan 35—9001.

l. Skerbele and Lassettre 65-9040.

m. Herzberg and Ramsay 52—7001; Ramsey 53—7003. Gordon, Mulac and Nangia 71-0169 (pulsed radiolysis).

n. Okabe and Lenzi 67-7484.

o. Adrian. .62-5011 (in argon at 4.2 K); Marx. 68-5178; Smith. (70—0335) ( 14 NH2 , 14 ND2 , 15 NH2 , I5 ND2). p. Meaburn and Gordon 68—0101 (pulsed radiolysis); Husain and Norrish 63—7008; Ramsay 53—7003.

q. Okabe and Lenzi 67—7484; Becker and Welge 63-6002.

20
Table A. 1.2. Properties of ionic species1

Ion AH{ ° (298.2 K)

(kcal/mol)

A.P.

(eV)

Relative abundance

(2 x 10

-7 torr) Comments

NH/ 154 (55-9002) 0 Accounts for 97% of positive ions at

1 torr (66—0298) because of rapid

ion— molecule reactions. Solvated at normal temperatures and pressures (66-9067, 68-0032, 64-9015, 65-0775,

71-9024).

nh3 + 223 10.2 100 Rapidly converted to NH4

+ at P near

1 torr (66-0298).

nh2 + 304 16.0 40.92 Rapidly converted to NH4 + at P near

1 torr (66-0298).

NH+ 382 17.1 (+H2 ) 21.6 (+2H)

4.50 See table 2.1 for reactions of NH+

.

a. Unless otherwise indicated values have been taken from the following sources. Standard heats of formation

(AHf °) and appearance potentials (A.P.), Wagman 68—9060; relative abundances, Melton 66—0298.

21
Appendix 2. Additives Used in Studies of Ammonia Radiolysis

Tables A.2.1 and A.2.2 are intended primarily as an index to the additives that have been

employed in studies of the radiation chemistry of gaseous ammonia. No attempt has been made to include detailed results; however, a number of these additives have been given rather extensive

consideration in section 2. Tables A.2.1 and A.2.2 do not include studies of additives employed

exclusively for purposes of synthesis (viz., synthesis of amines).

Table A.2.1. Additives: Binary mixtures

Additive Concn. range, mol % Radiation Comments Reference

Argon 0 1 00© “Co—y and fast e

_ Efficient energy transfer from

Ar to NH3.

Sorokin. 65—0523

Benzene 0-> 4.3

60 /-' Co—y Used to determine g(H2

). See table 2.2.3. Carstensen67-0701

Benzene 3.0

60 nCo—y ditto. Johnson. 68—0659 Benzene 0 -* 7.4

60 /~> Co—y ditto. Eyre. 70—0479

Carbon

tetrachloride

2 -> 9 “Co-y Used to study ion—neutralization. See section 2.1.1. Nishikawa. 68-0051

Carbon

tetrachloride 0-> 5 “Co-y ditto. Eyre. 70-0479

Cyclohexane 0 - 6.5

60 /-Co-y Used to determine g(H).

See section 2.2.1.

Eyre. 70-0479

Deuterium o t 8 1 MeV e

- G(HD) from NH3 -D2 used to est- imate g(H). See section 2.2.1.

Jones. 67—0270

Deuterium 0 -» 4.7

60 /—Co—y Suggest chain reaction involved

in production of HD.

Johnson. 68—0659

Ethylene 0 -* 7 1 MeV e Used to determine g(H2

). See table 2.2.3.

Jones. 67—0270

Ethylene 2 -* 4

60 /-Co—y ditto. Also used C2 D4

. Nishikawa. 68—0051

Ethylene 0 -> 3 250 keV e" Pulse radiolysis. Decreases

t 05 for decay of NH.

Meabum.68—0101

Hydrazine 0 —» 1.3 at 600 torr 0 —

4 at 200 torr

1 MeV e

_ Used to determine g(H). See

section 2.2.1.

Jones. 67—0270

Hydrazine 0 1

60 /-Co-y ditto. Carstensen67—0701 Hydrazine 5.3 and 7.4

60 /-Co—

y

Very limited study. Nishikawa. .69—032(

Hydrazine 0-> 2.2 Co—y Used to determine g(H) Eyre. 70—0479

Hydrogen 9 —» 50 0.8 MeV *H

+ Results are not consistent, but some indication that G(—NH3 ) decreases at high concn. of H2

.

Horscroft 64—0174

Hydrogen 12 -* 90 4He2+ (Rn) G(—NH3 ) decreases but relatively high concn. of H2 required.

Jungers32-0002

Iso-propanol 0 -> 4.3 "Co-y Used to determine g(H). See

section 2.2.1.

Eyre. 70-0479

Krypton ~ 90 2 MeV 2 H

+ N2 H4 only product studied. Lampe...63—0098

Methanol 0 10 “Co—

y

Used to determine g(H). Carstensen67—0701 Methanol 0 -» 8.3

60 /-Co-y ditto. Eyre. 70-0479

Neon 0 - 60 “Co-y and

fast e

_ * Efficient energy transfer from

Ne to NH3

.

Sorokin. 65—0523

Neon ~ 90 2 MeV 2 H

+ N2 H4 only product studied. Lampe...63—0098

Nitrogen 6 -» 50 0.8 MeV ‘H+ Energy transfer from N2 to NH3 at high N2 concns. Horscroft64—0 1 74

Nitrogen 17 -> 99 4 He2+ (Rn) Energy transfer from N2 to NH3 at high N2 concns. Jungers32—0002

Nitrous Oxide 0 - 10 “Co-y Used to study ion—neutralization. See section 2.1.1. Nishikawa. 68—0051

Nitrous Oxide 0 -> 100 “Co-y ditto. Johnson. 68—06r

<9 22
Table A. 2.1. Additives: Binary mixtures — Continued

Additive Concn. range, mol % Radiation Comments Reference

Nitric Oxide 0 13 >* 1o SCJ Reduced G(H2 ) to 0.69. G(N2 ) =

11.9 and presumably G(N2 ) =

g(NH) + g(NH2

).

Eyre. 70-0479

0 ^ 0.7 2 MeV e Pulse radiolysis. Studied

effect of NO on decay of NH2 and NH. Calculate specific rates for NO + NH and NO + NH2

.

Gordon. .71-0169

Oxygen 0 —» 3 x 10'3 MCo-y G(H2 ) and G(N2 ) reduced. Carstensen67—0701 Oxygen 0 —» 6 250 keV e~ Pulse radiolysis, no yield data. Report reduction in t0 s for decay of NH in presence of 02

.

Meabum.68—0101

Phosphine 0 ^ 100 “Co-y Yields consistent with NH2 + PH3 -» NH3 + ph2 H + PH3 — H2 + PH2 2PH2 -» PH3 + PH

2PH -> P2 + H2.

Buchanan. 70-0653

Propane 0-> 6.6 Sn01** Used to estimate g(H). See

section 2.2.1 and also table A.2.2.

Johnson. 68-0659

Propane 0 -> 8.6

60/-.Co—

y

ditto. Nishikawa. .69—0326c Propane 0 -> 20 60/-.Co—

y

ditto. Find G(H2 ) depends upon

dose.

Eyre. 70-0479

Propylene 1.5 SCJ o1 Used to determine g(H2

). See table 2.2.3. Johnson. 68—0659

Propylene 0 3.8

60/—Co—

y

ditto. Nishikawa. .67—0263 Propylene 0 —» 5 sCJ o1 ditto. Sorokin. 64— 1757 Propylene o t Tf; 60/-.Co—

y

ditto. Eyre. 70-0479

Propylene 0 —» 9 fast e~

* ditto. Sorokin. 65—0523

Propylene 0-^8 1.0 - 1.7 MeV e" Pulse radiolysis. Very high

intensity.

Willis.. 69-0272

Propylene 0-^ 3.3 250 keV e" Pulse radiolysis. Results in increases in G(N2 H4 ) (0.07 to 0.18).

Meabum.68-0101

Propylene o T r-H o 2 MeV e~ Pulse radiolysis. Studied

effect of C3 H6 on decay of NH2. Gordon.. 71—0169

Sulfur hexafluoride 0-> 1.1 sCJ oI Very limited study. See also table A.2.2. Nishikawa. 69—0326

O T r-H o 2 MeV e Pulse radiolysis. Studied

effect of SF6 on decay of NH2. Used to estimate importance of ion—neutralization.

Gordon.. 71-0169

Xenon 0 - 56 0.8 MeV *H+ Efficient energy transfer from

Xe to NH3.

Horscroft64—0174

Xenon o t § “Co-y ditto. Sorokin. 65—0523 Xenon ~ 24 X-rays (40 kV) ditto. Guenther.37—0001

a. Energy not specified.

b. See also 67-0263.

c. See also 68—0505 and 69—0326.

23
Table A. 2. 2. Additives : Ternary mixtures

Additives Concn. range, mol % Radiation Comments Reference

H2 and N 2 H2

: 0 ^ 75 N 2

: 0 ^ 25

4 He2+ (Rn) — Jungers32-0002

C3 H8 and N2 0 C 3 H8

: 0 ^ 12 N 2 0; 1.5 and 3.0 “Co-y See section 2.2.2. Johnson. 68—0659

C 3 H8 and N 2 0 C 3 H8

: 1 -* 4 Nz O: 5

60/-.Co—

y

See section 2.2.2. Nishikawa. .69— 0326

C3 H8 and SF6 C3 H8

: 1.5 SF6

: 0.2

60 pCo—

y

See section 2.2.2. Johnson. 68-0659*

C 3 H8 and SF6 C,H8

: 3.6 SF6

: 0 -> 1.6

60/-.Co-y See section 2.2.2. Nishikawa. .69-0326

iso— propanol + N2 0

iso—propanol: 0.5%

N2 0: O -* 1.7%

60pCo—

y

See section 2.2.2. Eyre. 70-0479

iso-propanol + sf6iso— propanol: 0.5%

SF6: 0 1.3%

60^Co-y See section 2.2.2. Eyre. 70-0479

iso— propanol +

CC14

iso— propanol: 0.5%

CC14

: 0 -* 1%

60 rCo—

y

See section 2.2.2. Eyre. 70-0479

a. See also 67—0369.

The author is profoundly indebted to Dr. Alberta Ross of the Radiation Chemistry Data

Center, University of Notre Dame for her generous and most valuable assistance in preparation of

this data review. The many helpful editorial comments of Dr. Lewis Gevantman of the National

Bureau of Standards are also gratefully acknowledged.

References

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E., LE RADIUM 11, 289-98 and 332-47

(1919).

32-0002 Decomposition et synthese de T ammoniac

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J.C., BULL. SOC. CHIM. BELGES. 41,

377-98 (1932).

32—7001 The photochemical decomposition of

ammonia. Wiig, E.O., Kistiakowsky, G.B.

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34-0001 The ion yield in the decomposition of

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34—0003 Influence de Tintensite d'irradiation, de la pression, de la vapeur de mercure et de la nature des parois sur la decomposition

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34—0005 The rate of recombination of atomic

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34—7002 Die Kinetik der photochemischen

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56,318-23 (1934).

34—

9002 Formation of negative ions in gases by

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35-

0002 The recombination of hydrogen atoms.

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35-7002 Photochemical investigations. I. The

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SOC. 57, 1559-62 (1935).

35—9001 The ultraviolet absorption spectrum of

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47, 822-7 (1935).

24
36-

0001 The radiochemical decomposition of deutero—ammonia. Jungers, J.C., J. PHYS. CHEM. 40, 155-8 (1936).

37-

0001 Hat die Lebensdauer von Gasioner einen

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37-

7002 Photochemical investigations. III. The

effect of cell size on the quantum yield for

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38-

0002 Effect of electric fields on the

decomposition of ammonia by alpha—rays. Smith, C., Essex, H., J. CHEM. PHYS. 6,

188-96 (1938).

38—

9001 Recombination of hydrogen atoms. Ill Amdur, I., J. AM. CHEM. SOC. 60,

2347 - 55 (1938).

39—

7001 On the photochemical decomposition of

ammonia. Shida, S., REV. PHYS. CHEM.

JAPAN 13, 12-30 (1939).

42—0001 Effect of strong electric fields on the

radiochemical decomposition of gaseous

ammonia. McGuinness, M.J., Jr., Essex, H.,

J. AM. CHEM. SOC. 64, 1908-11 (1942).

44—7000 Recherches sur la photolyse de

l'ammoniac. Vanpee, M., BULL. SOC.

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52—

7001 Absorption spectrum of free NH2 radicals.

Herzberg, G., Ramsay, D.A., J. CHEM.

PHYS. 20, 347 (1952).

53—

0008 Arbeit pro Ionenpaar von mehratomigen

Casen fuer Po—a—Teilchen. Biber, C.,

Huber, P., Mueller, A., HELV. PHYS.

ACTA. 26, 602 (1953).

53—

7003 The absorption spectra of free NH and

NH2 radicals produced by the flash

photolysis of hydrazine. Ramsay, D.A., J. PHYS. CHEM. 57, 415-7 (1953).

54—

7002 The photolysis of ammonia at 1849 A in a flow system. McDonald, C.C., Kahn, A.,

Gunning, H.E., J. CHEM. PHYS. 22(5),

908-16 (1954).

54-9005 Oxidation of hydrazine in solution. Cahn,

J.W., Powell, R.E., J. AM. CHEM. SOC.

76, 2568-70 (1954).

54-9006 Photoionization and total absorption cross

section of gases. I. Ionization potentials of

several molecules. Cross sections of NH3 and NO. Watanabe, K., J. CHEM. PHYS.

22(9), 1564-70 (1954).

55-0010 Effect of variations in source intensity on

the alpha induced decomposition of

ammonia. Burtt, B.P., Baurer, T., J. CHEM. PHYS. 23, 466-70 (1955).

55—7001 Decomposition of ammonia

photosensitized by mercury 6(

3 P0 atoms.

McDonald, C.C., Gunning, H.E., J. CHEM. PHYS. 23(3), 532-41 (1955).

55—9002 Thermodynamic properties of the

ammonium ion. Altshuller, A.P., J. AM.

CHEM. SOC. 77, 3480-1 (1955).

57—

0018 Alpha—induced decomposition of

ammonia. II. Effects of variations in

intensity and pressure. Burtt, B.P.,

Zahlan, A.B., J. CHEM. PHYS. 26(4),

846-50 (1957).

58—

0051 Behavior of some polyatomic gases in

nuclear reactors. Dolle, L., Proc. of

Second U.N. Internat. Conf. Peaceful

Lses Atomic Energy, Geneva 29. 367—74

(1958). (Publ. 1959).

58—

9004 Diimide-identification and study by mass

spectrometry. Foner, S.N., Hudson, R.L.,

J. CHEM. PHYS. 28, 719-20 (1958).

59—

9003 Reactions of gaseous ions. Ammonium

formation in ionized ammonia. Dorfman,

L.M., Noble, P.C., J. PHYS. CHEM. 63,

980-2 (1959).

61—0103 Nitrous oxide as a dosimeter for ionizing

radiations. Hearne, J.A., Hummel, R.W.

RADIATION RES. 15, 254-67 (1961).

61—

9008 Avarmenko, L.I., Kolesnitova, R.V., IZV.

AKAD. NAUK., S.S.S.R. OTDEL KHIM.,

NAUK., 1971 (1961).

62—

0074 Effect of density in radiolysis of ammonia.

Toi, Y., Peterson, D.B., Burton, M., RAD.

RES. 17, 399-407 (1962).

62—0131 Reactions of hydrogen atoms with

hydrazine, ammonia, and nitrous oxide.

Schiavello, M., Volpi, G.G., J. CHEM.

PHYS. 37(7), 1510-3 (1962).

62—0132 Vacuum ultraviolet photochemistry. III. Primary processes in the vacuum

ultraviolet photolysis of water and

ammonia. McNesby, J.R., Tanaka, I., Okabe, H., J. CHEM. PHYS. 36(3), 605-7

(1962).

62—5011 ESR studies of inorganic free radicals in

photolytic systems. Adrian, F.J., Cochran,

E.L., Bowers, V.A., ADVAN. CHEM.

SER. 36, 50-67 (1962).

62—7002 Blitzlicht-Photolyse des NH3 im

Vakuum-Ultraviolett. Bayes, K.D.,

25
Becker, K.H., Welge, K.H., Z. NATURFORSCH. PT. A 17, 676-80

(1962).

62—9017 Bond energies ionization potentials and

electron affinities. Vedeneyev, V.I.,

Gurvich, L.V., Kondrat'yev, V.N.,

Medvedev, N.A., Frankevich, Ye. L., St. Martin's Press, Edward Arnold

Publishers, New York, 202 pp., (1966).

62—

9019 Experimental determination of the

electron affinities of inorganic radicals.

Page, F.M., ADVAN. CHEM. SER. 36,

68-75 (1962).

63—

0098 Hydrazine formation in the gas—phase

radiolysis of ammonia. Lampe, F.W.,

Weiner, E.R., Johnston, W.H., Koski,

W.S., INTERN. J. APPL. RADIATION

ISOTOPES 14, 231-5 (1963).

63—0149 Bhtzhcht—Photolyse des NH3 im

Vakuum—UV (II)., Stuhl, F., Welge, K.H.,

Z. NATURFORSCH. PT. A 18, 900-6

(1963).

63—0150 Ion—molecule reactions in gaseous

ammonia. Derwish, G.A.W., Galli, A.,

Giardini—Guidoni, A., Volpi, G.G., J. CHEM. PHYS. 39(6), 1599-605 (1963).

63-0165 The gamma radiolysis of ammonia and the

methylamines in the gas phase. Schiek,

R.C., Thesis, Univ. of New Hampshire,

73 pp. (1963).

63-0167 Mass spectral studies of kinetics behind

shock waves. II. Thermal decomposition

of hydrazine. Diesen, R.W., J. CHEM.

PHYS. 39(9), 2121-8 (1963).

63—6002 Fluoreszenz von NH—Radikalen bei der

Photodissoziation des NH3 im Vakuum—

UV. Becker, K.H., Welge, K.H., Z. NATURFORSCH. PT. A 18, 600-3 (1963).

63—7008 The explosive oxidation of ammonia and

hydrazine studied by kinetic spectroscopy.

Husain, D., Norrish, R.G.W., PROC.

ROY. SOC. (LONDON). SER. A 273,

145-64 (1963).

63-9010 Reactions of nitrogen—hydrogen radicals.

I. NH2 recombination in the

decomposition of ammonia. Hanes, M.H.,

Bair, E.J., J. CHEM. PHYS. 38(3), 672-76

(1963).

63-

9014 Kinetics of three—body atom

recombination. Kretschmer, C.B.,

Petersen, H.L., J. CHEM. PHYS. 39(7),

1772-8 (1963).

64—

0174 Proton irradiation of ammonia. Horscroft,

R. C., TRANS. FARADAY SOC. 60, 323-

34 (1964).

64—0177 Gas—phase dosimetry by use of ionization

measurements. Meisels, G.G., J. CHEM.

PHYS. 41(1), 51-6 (1964).

64—0288 Recombination of hydrogen atoms in the

presence of atmospheric gases. Larkin,

F.S., Thrush, B.A., DISC. FARADAY

SOC. 37, 112-7 (1964).

64—1757 Decomposition of ammonia by y—

radiation. Sorokin, Yu. A., Pshezhetskii,

S. Ya., RUSS. J. PHYS. CHEM. 38(3),

434—6 (1964). Translated from, ZH. FIZ.

KHIM. 38(3), 798-801 (1964).

64—7002 Recombination and disproportionation of

NH2 radicals. Salzman, J.D., Bair, E.J., J. CHEM. PHYS. 41, 3654-5 (1964).

64-7003 Die Primaerprozesse der NH3 -Photolyse

bei 1470 A. Groth, W., Okabe, H.,

Rommel, H.J., Z. NATURFORSCH. PT.

A 19, 507-8 (1964).

64—7008 Vacuum ultraviolet photochemistry.

McNesby, J.H., Okabe, H., ADVAN.

PHOTOCHEM. 3, 157-240 (1964).

64—9015 Ion clusters in the ammonia glow

discharge. Dawson, P.H., Tickner, A.W.,

J. CHEM. PHYS. 40, 3745-7 (1964).

64-

9016 Decomposition of sulphur hexafluoride in

flames by reaction with hydrogen atoms.

Fenimore, C.P., Jones, G.W., COMBUST.

FLAME 8(3), 231-4(1964).

65—

0523 Kinetics and sensitisation of the radiolysis

of ammonia in the gas phase under the

action of fast electrons. Sorokin, Yu. A.,

Pshezhetskii, S.Ya., RUSS. J. PHYS.

CHEM. (ENGLISH TRANSL.). 39(8),

1037—40 (1965). Translated from, ZH. FIZ.

KHIM. 39, 1955-9 (1965).

65—0555 The determination of the rate constants

for the reactions between hydrogen and

oxygen atoms and ammonia molecules.

Aganesyan, K.T., Nalbandyan, A.B.

DOKL. PHYS. CHEM. PROC. ACAD.

SCI. USSR (ENGLISH TRANSL.). 160(1),

18-21 (1965). Translated from, DOKL.

ACAD. NAUK SSSR. 160(1), 162-5 (1965).

65-0775 Mass-spectrometric study of ions at near—atmospheric pressure. II. Ammonium ions produced by the alpha

radiolysis of ammonia and their solvation

in the gas phase by ammonia and water

molecules. Hogg, A.M., Kebarle, P., J. CHEM. PHYS. 43(2), 449-56 (1965).

26
65-9040 Electron—impact spectra. Skerbele, A.,

Lassettre, E.N., J. CHEM. PHYS. 42(1),

395-401 (1965).

65-9041 Reactions of hydrogen atoms in the gas

phase. Thrush, B.A., PROGR.

REACTION KINETICS 3, 65-95 (1965).

65-9044 The gas-phase decomposition of

hydrazine and its methyl derivatives.

Eberstein, I.J., Glassman, I., Proc. of the

Tenth Symposium (International) on Combustion, Combustion Institute,

Pittsburgh, Pa., pp. 365—74 (1965).

65-9046 The reaction of hydrogen atoms with

nitrous oxide. Dixon—Lewis, G., Sutton,

M.M., Williams, A., J. CHEM. SOC.

5724-9 (1965).

65-

9048 The chemistry of diimine. Huening, S.,

Mueller, H.R., Thier, W., ANGEW.

CHEM. INT. ED. ENGL. 4(4), 271-82

(1965).

66—

0201 Protron transfer and neutralization

reactions in irradiated gases at atmospheric pressure and between —78°

and 25° C. Lawrence, R.H.Jr., Firestone,

R.F., ADVAN. CHEM. SER. 58, 278-90

(1966).

66-0249 Evidence for thermal hydrogen— atom

reactions in irradiated gaseous HC1.

Davidow, R.S., Lee, R.A., Armstrong,

D.A., J. CHEM. PHYS. 45(9), 3364-9

(1966).

66-0298 Study by mass spectrometry of the

decomposition of ammonia by ionizing

radiation in a wide-range radiolysis source. Melton, C.E., J. CHEM. PHYS.

45(12), 4414-24 (1966).

66—0434 Nitrous oxide dosimetry. Effects of

temperature, pressure, and electric field. Jones, F.T., Sworski, T.J., J. PHYS.

CHEM. 70(5), 1546-52 (1966).

66-8024 Computer program for the kinetic

treatment of radiation—induced

simultaneous chemical reactions.

Schmidt, K.H., ANL-7199, 51 pp. (Apr.

1966).

66-9067 Ion-solvent molecule interactions studied

in the gas phase. Heats and entropies of

individual steps. NH4 + -(n— 1)NH3 + NH3 = NH4 + -nNH3 Hogg, A.M., Haynes, R.M.,

Kebarle, P., J. AM. CHEM. SOC. 88(1),

28-31 (1966).

66-9068 Reactions of thermal energy ions. Part 4. Ion molecule reactions in ammonia and

hydrazine. Harrison, A.G., Thynne, J.C.J.,

TRANS. FARADAY SOC. 62, 2804-14

(1966).

67—0027 Surface catalytic effects in nitrous oxide

radiation dosimetry. Lampe, F.W., Kevan,

L., Weiner, E.R., Johnston, W.H., J. PHYS. CHEM. 71(5), 1528-9 (1967).

67—0093 Primary processes in the formation of

hydrogen atoms in the radiolysis of water

vapor. Johnson, G.R.A., Simic, M., J. PHYS. CHEM. 71, 1118-23 (1967)..

67—0263 Effect of hydrogen atom and electron

scavengers on the gas—phase radiolysis of

ammonia. Nishikawa, M., Shinohara, N.,

Matsuura, N., BULL. CHEM. SOC.

JAPAN 40(8), 1993 (1967).

67—0270 Radiation chemistry of gaseous ammonia.

Part I. Radical and molecular product

yields. Jones, F.T., Sworski, T.J.,

TRANS. FARADAY SOC. 63, 2411-25

(1967).

67—0271 Radiation chemistry of gaseous ammonia.

Part 2. Hydrazine formation. Jones, F.T.,

Sworski, T.J., Williams, J.M., TRANS.

FARADAY SOC. 63, 2426-34 (1967).

67-0369 Effect of hydrogen atom and electron

scavengers on the radiolysis of ammonia

gas. Johnson, G.R.A., Simic, M.

NATURE 216(5114), 479-80 (1967).

67—0546 The effect of temperature and pressure on

the vapour phase y—radiolysis of some

polar molecules. Anderson, A.R., Winter,

J.A., The Chemistry of Ionization and

Excitation, Johnson, G.R.A. and Scholes,

G. (ed.)., Taylor and Francis Ltd, London,

pp. 197-209 (1967).

67—0701 The radiation chemistry of gaseous

ammonia. Carstensen, J.T., Thesis,

Stevens Inst, of Technology, Hoboken,

N.J., 148 pp. (1967).

67—7484 Photodissociation of NH3 in the vacuum

ultraviolet. Okabe, H., Lenzi, M., J. CHEM. PHYS. 47(12), 5241-6 (1967).

67-9004 Mass—spectrometric and theoretical

evidence for NH4 and H3 0. Melton, C.

Joy, H.W., J. CHEM. PHYS. 46(11),

4275-83(1970).

67-9079 Reactions of thermal energy ions. VI.

Hydrogen-transfer ion—molecule reactions

involving polar molecules. Gupta, S.K.,

Jones, E.G., Harrison, A.G., Myher, J.J., CAN. J. CHEM. 45, 3107-17 (1967).

27
67—9108 An evaluation of kinetic rate data for

reactions of neutrals of atmospheric

interest. Schofield, K., PLANET. SPACE

SCI. 15, 643-70 (1967).

67—

9109 Ammonia decomposition in glow

discharge. Carbaugh, D.C., Munno, F.J.,

Marchello, J.M., J. CHEM., PHYS. 47(12),

5211-4 (1967).

68—

0032 Ion—solvent—molecule interactions in the

gas phase. Enthalpies and entropies for

the reactions NH4 + (NH3 ) n_ 1 + NH3 = NH4 + (NH3 ) n

. Searles, S.K., Kebarle, P., J. PHYS. CHEM. 72(2), 742-3 (1968).

68—0051 Gas—phase radiolysis of ammonia, Effect

of density and additives. Nishikawa, M.,

Shinohara, N., RADIATION RES. 33,

194-203 (1968).

68—0101 Pulse radiolysis of ammonia gas - rate of

disappearance of the NH triplet radical.

Meaburn, G.M., Gordon, S., J. PHYS.,

CHEM. 72(5), 1592-8 (1968).

68—0318 The dosimetry of very high intensity

pulsed electron sources used for radiation

chemistry. II. Dosimetry for gaseous

samples. Willis, C., Miller, O.A.,

Rothwell, A.E., Boyd, A.W., ADVAN.

CHEM. SER. 81, 539-49 (1968).

68-0505 On the yield of hydrogen atoms in the

vapor phase radiolysis of ammonia.

Nishikawa, M., Kuroda, K., Matsuura, N.,

BULL. CHEM. SOC. JAPAN 41(5), 1276

(1968).

68-0555 Radiolysis of gaseous ammonia.

Kazanjian, A.R., Brown, A.K., RFP 1089,

7pp., 22 Nov. 1968 (Dow Chemical Co.,

Rocky Flats Div., Golden, Colo.).

68-0650 Organic gases. Meisels, G.G.

Fundamental Processes in Radiation

Chemistry, Ausloos, P.(ed.)., (Interscience

Publishers, New York, 1968) pp. 347—411.

68-0659 Primary processes in the radiolysis of

gaseous ammonia. Johnson, G.R.A.,

Simic, M., ADVAN. CHEM., SER. 82,

197-211 (1968).

68-5013 The measurement of the rate of

recombination of hydrogen atoms at room

temperature by means of e.s.r. spectroscopy. Bennett, J.E., Blackmore,

D.R., PROC. ROY SOC. (LONDON). A

305, 553-74 (1968).

68-5178 ESR study of free radicals produced in

the gas phase by low energy electrons.

Marx, R., Mauclaire, G., ADVAN. CHEM.

SER. 82, 212-21 (1968).

68-7069 Ion—molecule reactions of NH3 + by

photoionization. Chupka, W.A., Russell,

M.E., J. CHEM. PHYS. 48(4), 1527-33

(1968).

68—7168 The photolysis of ammonia at 2062 A in

the presence of propane. Groth, W.E.,

Schurath, U., Schindler, R.N., J. PHYS.

CHEM. 72(11), 3914-20 (1968).

68—7214 Reactions of nitrogen—hydrogen radicals.

III. Formation and disappearance of NH

radicals in the photolysis of ammonia.

Mantei, K.A., Bair, E.J., J. CHEM.

PHYS. 49(7), 3248-56 (1968).

68—

9060 Selected values of chemical

thermodynamic properties, tables for the

first thirty—four elements in the standard

order of arrangement. Wagman, D.D.,

Evans, W.H., Parker, V.B., Halow, I., Bailey, S.M., Schumm, R.H., NBS Technical

Note 270—3, January, 1968. 264p. (Natl.

Bureau of Standards).

69-

0026 Effect of additives in the radiolysis of

gaseous ammonia at high densities.

Nishikawa, M., Kuroda, K., Matsuura, N.,

BULL. CHEM. SOC. JAPAN 42(1), 116-

18 (1969).

69—0085 Effect of density and electron scavengers

in nitrous oxide radiolysis. Sears, J.T., J. PHYS. CHEM. 73(4), 1143-46 (1969).

69—0272 Primary yields and mechanism in the

radiolysis of gaseous ammonia. Willis, C.,

Boyd, A.W., Miller, O.A., CAN. J. CHEM. 47(16), 3007-16 (1969).

69-0326 The yield of hydrogen atoms in the vapor

phase radiolysis of ammonia. Nishikawa,

M., Kuroda, K., Matsuura, N., BULL.

CHEM. SOC. JAPAN 42(7), 1783-6 (1969).

69-7017 The photolysis of ammonia at 2062 A in

the presence of ethylene. Schurath, U.,

Tiedemann, P., Schindler, R.N., J. PHYS.

CHEM. 73(2), 456-9 (1969).

69-

9067 Ionization potentials, appearance

potentials, and heats of formation of

gaseous positive ions. Franklin, J.L.,

Dillard, J.G., Rosenstock, H.M., Herron,

J.T., Draxl, K., Field, F.H., NSRDS-NBS

26 - June 1969, 285p. (Natl. Bureau of

Standards).

70—

0134 A comparative study of the gas— phase

radiation chemistry of phosphine and

ammonia. Buchanan, J.W., Hanrahan,

28
R.J., RADIATION RES. 42(2), 244-54

(1970).

70—0335 Electron spin resonance spectra of 15 N

labelled amino radicals. Smith, D.R.,

Seddon, W.A., CAN. J. CHEM. 48, 1938-

42 (1970).

70—0479 Primary yields in the y radiolysis of

ammonia. Eyre, J.A., Smithies, D.

TRANS. FARADAY SOC. 66(9), 2199-

209 (1970).

70—0563 Ionic collision processes in gaseous

ammonia. Ryan, K.R., J. CHEM. PHYS.

53(10), 3844-8 (1970).

70—0653 The radiation chemistry of phosphineammonia mixtures in the gas phase.

Buchanan, J.W., Hanrahan, R.J. RADIATION RES. 44(2), 296-304 (1970).

70—7065 Ratio of disproportionation to combination

of N2 H3 radicals. Stief, L.J., J. CHEM.

PHYS. 52(9), 4841-5 (1970).

70—9007 Bond dissociation energies in simple

molecules. Darwent, B.deB., NSRD—NBS

31, 1970, 48p. (Natl. Bureau of Standards).

70—9010 Rate constants for gas phase reactions.

Handbook. Kondratiev, V.N., Izd "Nauka",

Moscow, 1970, 351p. (RUS).

71-0002 Ion lifetimes in gaseous ammonia. Wilson,

D.E., Armstrong, D.A., J. PHYS CHEM.

75, 444-5 (1971).

71-0062 Radiation chemistry of ethanol: A review of

the yields, reaction rate parameters, and

spectral properties of transients, Freeman,

G. R., NSRDS-NBS 48, in press.

71-0169 Pulse radiolysis of ammonia gas. II. Rate

of disappearance of the NH2 (X2 B1 ) radical.

Gordon, S., Mulac, W., Nangia, P., J. PHYS. CHEM. 75(14), 2087-93 (1971).

71-0179 Radiation chemistry of nitrous oxide gas:

Primary processes, elementary reactions and

yields, Johnson, G. R. A., NSRDS-NBS 45,

in press.

71—0216 A re-examination of the yields in the high

dose rate radiolysis of gaseous ammonia.

Boyd, A.W., Willis, C., Miller, O.A.

CAN. J. CHEM. 49(13), 2283-9 (1971).

71—9024 Ion—molecule reactions in NO—NH3 mixtures. Puckett, L.J., Teague, M.W.

BRL R 1521, Jan. 1971, 30p.

29
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4. TITLE AND SUBTITLE

The Kadi ation Chemistry of Gaseous Ammonia

5. Publication Date Jebruary 1974

6. Performing Organization Code

7. AUTHOR(S)

Donald B. Peterson

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16. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here.) H2 and N2 are the only significant products of radiolysi s

i of gaseous ammonia under

static conditions at dose rates less than about 10'L ^eV*g“1

s”

u

‘; and G(H2) = 5.0±1.0 and

G(N2) = 1*7^ 0*3 for irradiation at 20 G and pre ssuresnear one atmosphere. Yields do not

appear to depend significantly upon L3T (linear energy transfer); and they are independent of dose up to at least 8 x 10 eV/g. In static systems at dose rates-^ 10^^eV*g“^s”

and in flow systems, N2H4 is also a product.

At dose rates less than 10^9eV*g“^s”^ , G(-NH?) increases markedly with temperature

and reaches a plateau value of about 10 at temperatures near 150 - 200° C. At very high

dose rates (^ 10 ''eV»g“^s"^) G(-NH^) increases significantly at higher temperatures

(value depends upon dose rate) and G(-NHj) does not appear to be leveling off at the

highest temperature studied ( 460 C) . In both dose rate regions the increase in Gt-UH^)

is attributed primarily to the increasing importance of NH-z + E —>NH2 4- Hg with increasing temperature. G(-EH^) also appears to increase wiTh decreasing dose rate.

However, the effect is less pronounced than the effect of temperature, and the experimental evidence is not unequivocal.

UH and HK2 have been observed spectroscopically in pulse radiolysis of NHjand such

studies lead to g(NH) = 0.4. However, this value of g(NH) is low because of errors in

dosimetry. g(NH2) was h°t obtained directly because the absorptivity of HHg was not

available. A number of additives has been employed in attempts to determine primary

yields of other species involved in radiolysis; however, results with different additives and from different laboratories are in good agreement only in the case of

17. KEY WORDS (Alphabetical order, separated by semicolons) Ammonia; chemical kinetics ; data compilation; G; g; gas; radiation chemistry; rates; review.

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Abstract (continued')

g(H2) (0.7 - O.S) and g(HHi++

) < 3.3 - 3*9)* The best value of g(H) appears to be 10.4 ^ 0.6; and this is the preferred value. g(NHg) is obtained from the material balance

g(H)+ 2g(H2 ) =• g(NHpJf 2g(KH) # The preferred value of g(HH) is 0.75, i»e, g(KH)

g(Hg) and this leads to g( NHg) — 10. 4.

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