ST U,

NSRDS

?*C£ D ftT ^

DEPARTMENT

OF

COMMERCE

National

Bureau

of

Standards

Radiation Chemistry

of Nitrous Oxide Gas

Primary Processes,

Elementary Reactions,

and Yields

i

Radiation Chemistry of Nitrous Oxide Gas

Primary Processes, Elementary Reactions,

and Yields

G. R. A. Johnson

Department of Chemistry

University of Newcastle upon Tyne

Newcastle upon Tyne, NEI 7RU

Newcastle, England

Prepared at the Radiation Chemistry Data Center

Radiation Laboratory

University of Notre Dame

Notre Dame, Indiana 46556

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

NATIONAL BUREAU OF STANDARDS, Richard W. Roberts, Director

issued December 1973
Library of Congress Catalog Card Number: 72-600244

NSRDS-NBS 45

Nat. Stand. Ref. Data Ser., Nat. Bur. Stand. (U.S.), 45, 27 pages (Dec. 1973)

CODEN: NSRDAP

@1973 by the Secretary of Commerce on Behalf of the United States Government

U.S. GOVERNMENT PRINTING OFFICE

WASHINGTON: 1973

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

(Order by SD Catalog No. C 13.48:45). Price 60 cents. Stock Number 0303-01165
Foreword

The National Standard Reference Data System provides access to the quantitative data of physical science, critically evaluated and compiled for convenience and readily accessible through a variety of distribution channels. The System was established in 1963 by action of the President’s

Office of Science and Technology and the Federal Council for Science and Technology, and

responsibility to administer it was assigned to the National Bureau of Standards.

NSRDS receives advice and planning assistance from a Review Committee of the National

Research Council of the National Academy of Sciences-National Academy of Engineering. A number of Advisory Panels, each concerned with a single technical area, meet regularly to examine

major portions of the program, assign relative priorities, and identify specific key problems in need of further attention. For selected specific topics, the Advisory Panels sponsor subpanels

which make detailed studies of users’ needs, the present state of knowledge, and existing data re- sources as a basis for recommending one or more data compilation activities. This assembly of advisory services contributes greatly to the guidance of NSRDS activities. The System now includes a complex of data centers and other activities in academic insti- tutions and other laboratories. Components of the NSRDS produce compilations of critically

evaluated data, reviews of the state of quantitative knowledge in specialized areas, and computations of useful functions derived from standard reference data. The centers and projects also establish criteria for evaluation and compilation of data and recommend improvements in ex- perimental techniques. They are normally associated with research in the relevant field. The technical scope of NSRDS is indicated by the categories of projects active or being

planned: nuclear properties, atomic and molecular properties, solid state properties, thermodynamic and transport properties, chemical kinetics, and colloid and surface properties.

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 control, development of new materials for building and other technologies, measuring and correcting

environmental pollution depend on quality reference data. In NSRDS, the Bureau’s responsibility

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

2. Primary Processes

2.1. Electronic excitation

2.2. Ionization

2.3. Electron capture

3. Elementary Reactions

3.1. Neutral species

3.2. Positive ions

3.3. Negative ions

3.4. Neutralization reactions

4. Product Yields under Dosimeter Conditions

4.1. Nitrogen

4.2. Oxygen

4.2.1.

Oxygen and nitric oxide yields

4.3. Nitric oxide

4.4. Yields at very high dose rate

5. Effects of Conditions on Yields

5.1. Total dose

5.2. Pressure

5.3. Temperature

5.4. Electric fields

6. Effects of Additives on Yields

7. Rare Gas Sensitized Radiolysis

8. N2 O as Additive

9. References

1

11

2

3

3

3

3

4

5

6

6

7

8

9

9

10

10

11

12

13

14

15

15

17

v
List of Tables

Page Table 2.1. Threshold energies (eV) for N2 O decomposition (64-7008) ... 2

Table 2.2. Dissociation of neutral excited molecules in irradiated N2 O... 2

Table 2.3. Yields of primary ions from N2 O. 3

Table 3.1. Elementary reactions. Neutral species 4

Table 3.2. Elementary reactions. Positive ions 5

Table 3.3. Elementary reactions. Negative ions 6

Table 3.4. Ion neutralization reactions in irradiated N20 6

Table 4.1. Initial G(N2 ) (dose rate up to 1018eV g

-1

s _1

) 7

Table 4.2. Initial O2 yields (dose rates up to 1018eV g

-1

s -1

) 8

Table 4.3. Initial NO yield (dose rates up to 1018eV g

_1

s _1

) 9

Table 4.4. Yields from very high dose rates (pulsed irradiation) 10

Table 5.1. Dependence of yields on total dose 10

Table 5.2. Effect of N2 O pressure on yields at room temperature 11

Table 5.3.1. Dependence of yields on temperature 12

Table 5.3.2. Isotopic distribution in products from 15 N

14NO at different

temperatures 13

Table 5.3.3. Dependence of yields on temperature (high dose rate pulsed

irradiation) 13

Table 6.1. Limiting yields with various additives (A) at room

temperatures 14

Table 6.2. Isotopically labelled products from N2 O with 15 NO present

(65-0483) 14

Table 7. Rare gas sensitized radiolysis of N2 O (70-0413) 15

Table 8.1. G(N2 ) from gases containing N2 O as additive (organic

systems) 16

Table 8.2. G(N2 ) from gases containing N2 O as additive (inorganic

systems) 16

VI
Radiation Chemistry of Nitrous Oxide Gas

Primary Processes, Elementary Recations and Yields*

G.R.A. Johnson

University of Newcastle upon Tyne

Data on the radiation yields from nitrous oxide gas, and the effects of variables, including doserate, total dose, pressure, temperature, applied fields and scavengers are reviewed. The use of N2 0

as a gas-phase, chemical dosimeter is discussed. Primary processes in irradiated N2 0 are discussed

and elementary reactions, relevant to the system, are listed.

Key words: Chemical kinetics; data compilation; dosimetry; G; gas; nitrous oxide; radiation chemistry; rates; review.

1. Introduction

Although radiolysis of nitrous oxide was first studied over half a century ago (19-0001) a complete mechanism cannot yet be written. To a large extent, this is a consequence of the

complexity of the system and, at the present time, collection of the available data on nitrous oxide

cannot be justified either on the grounds of completeness or by the hope that the collection may

precipitate a full interpretation. Nevertheless, in spite of the many deficiencies and discrepancies

in present knowledge of the nitrous oxide system, the information available is of significance

because of the two important roles of nitrous oxide in radiation chemistry: as a gas—phase

chemical dosimeter and as a selective electron scavenger in a variety of systems. It is for this reason that this data survey has been prepared.

The aim is to present the available data on the radiation yields from nitrous oxide and on the

effects of important variables on the yields. The reactions which may occur in the system are

listed, with the information about their rate constants that is available from independent sources. No attempt is made here to interpret the yields in terms of a reaction mechanism.

The reference numbers are the reference code numbers assigned by the Radiation Chemistry

Data Center.

2. Primary Processes

2.1. Electronic Excitation

Much of the information about the chemical consequences of electronic excitation of N2 0 is obtained from spectroscopic and photochemical studies. The optical absorption spectrum is highly

structured in the region (123.6 to 184.9 nm) normally used for photochemical studies (53-9004),

suggesting that the excited states are not all dissociative. However, there is no evidence that

excited N2 0 molecules participate in the photochemistry prior to their dissociation.

*This is a data review prepared for, and in cooperation with, the Radiation Chemistry Data Center of the Radiation Laboratory, University of Notre Dame, 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
The electron impact excitation spectrum of N2 0 shows transitions corresponding to levels

observed in the optical spectrum; a forbidden transition, probably to a triplet state, was observed

at 4.4 eV (71-9364). The known photochemistry of N2 0 can be interpreted with reasonable success in terms of the primary reactions (1) and (2): N2 0 -> N2 + O (1)

N2 0 —> N + NO (2)

The products of these reactions can be in a variety of excited states. The threshold energies for

production of the different excited states are given in table 2.1. Recent experimental work using high dose rate electron pulses has given information about the

extent of the contribution of excitation processes to the net radiolytic decomposition (72-0088).

The conclusions are summarized in table 2.2.

TABLE 2.1. Threshold energies (eV) for N2 O decomposition (64-7008

N2 (N 2 0 —> N2 + O)

0 a

3 s; B3 n g a *n.

3p 1.67* 7.89 9.03 10.23 3.64 9.86 11.00 12.20

*S 5.86 12.08* 13.22* 14.11 NO (N 2 0 -> NO + N) 4

N x

2 n A2 S

+ b

2 n

4 S 5.02* 5.42* 5.61*

2 d 7.40 7.80 7.99

2 P 8.60 9.00 9.19

a. Optical transition is spin forbidden. D(NN-O) = 1.67 eV (67-9124) D(N-NO) = 4.99 eV (62-9017)

2.2. Ionization

Table 2.3 gives the yields of positive ions in N2 0, calculated from 1T(N2 0) = 32.9 ± 0.4 eV per

ion pair (64-0177) and the ion fragmentation pattern, determined in a low pressure mass

spectrometer at 70 eV (65-0483). This may not be a true representation of the radiolytic ion

yields, since the extent of fragmentation may be less at the higher pressures used in the

radiolysis. No information appears to be available from mass spectrometry at higher pressures.

Table 2.2 Dissociation of neutral excited molecules in irradiated N20 (Pulsed irradiation

at high dose rate (1026 — 1028 eV g

_1

s _1

) 72-0088)

Reaction G(reaction)/molecules (100 eV) 1

N2 0^ N2 (X1 S)+ 0(‘D) (or >S) 4.00 N2 0-+N2 (A3X)+0(3P) 0.81 N2 O^N(2 D) + NO 0.05

NOTE: These values were not measured directly but are derived from product yield measurements making several assumptions about the reaction mechanism. For a detailed discussion see reference 72-0088.

2
2.3. Electron Capture

The rate of electron capture by N2 0, the nature of this process and its chemical consequences

are still the subjects of active experimentation and discussion and clearly it will be some time

before the last word is said on these matters. Discussions of recent work can be found in

references 72—0449 and 72—9150.

It is generally agreed that, at least in the pressure region above about 20 torr. capture of thermal electrons occurs predominantly by a pseudo three body process (3) ( 68—9042, 68-9078'.

e" + 2 N2 0 (3)

The apparent rate constant kz = (2.01 ± 0.07) x 109 dm6 mol-2

s-2 (68—9042).

Attachment by a two—body dissociative process, reaction (3a)

e + N2 0 —> N2 + O (3a)

also occurs in X2 0. Recent rate measurements 1 72 — 0449 » give A*3 a =3.6xl06 dm3 mol-1

s -1

1 298

K). Reaction (3a) is 0.21 eV endothermic and it has been suggested that the zero energy capture

process might be due to attachment to the few N2 0 molecules with internal vibrational energy

above the threshold value (67—9124, 69—9031, 69—9136). The temperature dependence of precise

data in the range 278-355 K fits the relationship A' 3 a = 4.4 x 1013 exp <— 4.8xlO®/Ti dm3 mol-1

s _1

giving an activation energy for attachment of 0.42 ± 0.04 eV. These data, taken together with data

at high temperatures fit the relationship A*3a = 1.5 x 1013 exp — 4.6xl03 /T) dm3 mol-1s -1 over the

range 278-2900 K (72-0449).

The products from reactions (3) and (3a) are discussed in section 3.3.

Table 2.3. Yields of primary ions from NTO

Ion Accompanying G/molecules(100e\ 1 Neutral Species a b

N2 0

+ 1.98 1.90 NO+ N 0.61 0.59

N

+ NO 0.21 0.25 0

+ n2 0.09 0.10

Nj 0 0.15 0.21

e — 3.04 3.04

Note: \ alues based on ion pair yield calculated from the energy required per ion pair JT(N20)= 32.9 ±0.4 eV (64-0177) using mass spectral data from a '65-0483'. b ‘66-9163).

3. Elementary Reactions

The elementary reactions participating in N2 0 radiolysis can. at present, be deduced only by

making assumptions about the nature of the primary processes and of the reactive intermediates

given by such processes. The available information about the various possible intermediates is summarized in tables 3.1. 3.2, and 3.3. The extent to which any of these reactions is involved in

N2 0 radiolysis is not known and, of course, will depend to some extent on the reaction conditions.

3.1. Neutral Species

See table 3.1.

See table 3.2.

3.2. Positive Ions

3
Table 3.1. Elementary reactions. Neutral species at room temperature

Species Reaction Rate Constant/

dm3 mol

_1 s_1 (second order)

dm6 mol

-2 s~2 (third order)

s

-1 (first order)

Reference Note

0(

3 P) O + N2 0 —

N2 + 02 69-9080 a O + N2 0 -» 2 NO — 69-9080 a O + NO + M —» N02 + M 3.7 x 10

10 64-9021

O + N02 -+ NO + 02 2.1 x 10

9 57-7006

O + 02 + M -» 03 + M (M = N2 0) 5.4 x 10

8 68-9063

o + o + m^o2 + m 2.6 x 109 68-9063 d O + N(4 S) + M -» NO + M 4 x 10

9 67-9126 d 0(‘D) O* + N2 0 —> N2 + 02 4.2 x 10 10 68-7198 b 70-7558

O* + Nz O -» 2NO 7.8 x 10 10 68-7198 b O* + NO -> 0(

3 P) + NO 9 x 1010 68-7198

O* + 02 ^ 0(

3 P) + 02 2.4 x 1010 68-7198

0(

l S) O* + N2 0 -* 0(

3 P) + n2 o 9.6 x 109 68-7198

O* + NO —> 0(

3 P) + NO 3.3 x 1011 68-7198

N(4 S) N + N2 0-^ N2 + NO < 10

s 57-9008

N + NO -» N2 + O 1.8 x 10

10 69-9080 c N + N + M->N2 +M (M=N2 ) 3 x 10

9 67-9126 d N + O + M^NO + M (M=N2 ) 4 x 10

9 67-9126 d N(2 D) N* + N2 0 -* N2 + NO 1.8 x 109 69-6025

N* + NO -> N2 + 0(

3 P) 1.1 x 10

11 69-6025

N* + NO -» N(4 S) + NO < 3.6 x 106 69-6025

N2 ( 3 Su +

) N2 * -> N2 + hv 8.3 x 10“2 67-9127 n2 * + n2 o-> n2 + n2 o 3.8 x 10

9 69-7003 e N2 * + NO -> N2 + NO(A2 2) 4.2 x 10

10 69-7003

N2 ( 3 n g

) N2 * + N2 0-» 2N2 (

1 S) + 0(‘S) 9.6 x 10

10 69-7003 n2 * + no^- n2 + no 1.4 x 10

11 69-7003

a. Negligible at temperatures used in radiolysis.

b. Rate constants calculated from the absolute rate constant for deactivation of O^D) by H2 0 (68-7198)

and relative constants for the two reactions of 0(*D) with N2 0 (70-7558); cf. also 71-7213.

c. Recommended rate constant k = 3.1 x 10

10 exp (-334/RT) dm3 mol-1

s

-1 (R in cal mol-1 AT-1

). (69—9080).

d. No values reported for M = N2 0.

e. From quantum yield in N2 0 photolysis at 147 nm (71-7181) it is concluded that deactivation of N2 ( 3 £) by

N2 0 results in dissociation of N 2 0 (—> N2 + O). See 71—7181 for discussion of previous evidence for

this reaction.

3.3. Negative Ions

At very high dose rates electron capture by N2 0 does not compete effectively with ionelectron neutralization and negative ion reactions do not occur (72—0088).

At low dose rates, where electron capture can occur, the negative ion reactions may be of

considerable significance (65—0483, 70—0384, 72—0088, 72—0449, 72—9150). However, the negative

ion reactions in N2 0 are rather complicated and not well understood. For detailed accounts of the

information available references 72—0449 and 72—9150 should be consulted.

It has been suggested (68—9042) that N2 0~ might be formed by the three—body electron

capture reaction (3). This ion has not been directly observed as a product of electron capture,

although it has been observed in a mass spectrometer under conditions where it is formed as a

result of the reaction of O

- with N2 0 (66—9042). At low pressures (up to 20 torr) the third order

4
Table 3.2. Elementary reactions. Positive ions

Species Reaction Rate Constant /dm3 tnor 1 s -1 Reference Note

N2 0

+ N2 0

+ + N2 0 -» 2N2 + 02 + __ _ a N2 0

+ + N2 0 -*• N2 + NO+ + NO — 67-9129 b N2 0

+ + NO NjO + NO+ — — a n2 o

+ + o2 -» n2 o + 02 + — — a N2 + n2 + + n2 o^n2 + n2 o

+ 3.0 x 10 u

70-9074

N2 + + N2 0-» NO+ + N2 + N 2.4 x 10 u

70-9074

n2 + + o2 -^ n2 + o2 + 2.8 x 10

10 70-9074 n2 + + no-^-n2 + no+ 3.0 x 10u

70-9074

0

+ o

+ + n2 o ^ n2 o

+ + 0 2.4 x 10 u 70-9074 o

+ + n2 o^ o2 + + n2 1.2 x 1010 70-9074

0

+ + Nj^ NO+ + N 7.8 x 107 70-9074

0

+ + NO -> NO+ + O 1.5 x 1010 70-9074 o

+ + o2 ^ 02 + + 0 1.2 x 1010 70-9074

N

+ N

+ + N2 0 ^ NO+ + N2 3.0 x 1011 70-9074

N

+ + 02 + + N 3.0 x 10

11 70-9074

N

+ + 02 -* NO+ + O 3.0 x 10 n

70-9074

N

+ + NO -> NO+ + N 4.8 x 1011 70-9074

a. Reactions feasible on energetic grounds but no rate data reported.

b. Reaction cross-section 6.3 x 10

_17 cm

2

.

attachment process may be a consequence of the second order attachment reaction (3a) and a sequence involving the following negative ion reactions (72—9150):

O' + N2 0 -* NO" + NO

NO’ + N2 0 -» N2 0 + NO +e"

NO- + N2 0 NOj + N2 NO" + 2N2 0 N3 02 + N2 0

O

- + 2N2 0 —> N2 02 + N2 0

At high pressures (above 20 torr) it is necessary to postulate the formation, as a product of

reaction (3), of an ion which can detach an electron:

e + N2 O ^ N2 ON2 0- + n2 o*

^

n2 + O- + n2 o

(where N2 0* is a molecule with sufficient energy to make the forward reaction endoergic) (72—

9150).

The significance of the electron detachment reaction:

NO" + N2 0 NO + N2 0 + e- has been demonstrated (72-0449) and the possible contribution of the reaction:

O- + N2 0 NO- + NO

(followed by electron detachment from NO") to the chain decomposition of N2 0 at low

temperatures and high pressures has been discussed (72—0449). (See also sections 5.2 and 5.3.)

Elementary reactions of negative ions are collected in table 3.3.

3.4. Neutralization Reactions

Ion lifetime measurements in N2 0 indicate that ion clustering can complicate the

recombination process (70—0046, 72—9150) and this is of importance at low dose rates. Attempts

5
have been made to deduce information about the chemical consequences of ion neutralization at low dose rates by studying the effects of electron scavenging additives (70-0413). This approach

has not been successful, mainly because of a lack of knowledge of the effects of such additives on

reactions other than ion neutralization and also because the reactions of the negative species from

N2 0 are not understood.

Complications due to secondary reactions of the ions can largely be avoided by using very high

dose rates (72-0088). The main reactions occurring under these conditions are summarized in

table 3.4.

Table 3.3. Elementary reactions. Negative ions

Species Reaction Rate Constant /dm3 mol~1 s~

1

Reference Note

N2 0~ N2 0 + 02 —» 03 + N2 fast 69-9135

0“ O + N 2 0 —*• N2 + 0 2 — 64-9020 a O' + Nz O -* NO' + NO 1.2 x 10

11 68-9071

O' + N2 0 -* N02 " + N 2.4 x 10

8 66-9042 b O' + N2 0 -* N2 0' + O 1.2 x 10

10 66-9042

0 + no2 ^ N02 " + 0 6 x 10

11 66-9042

O' + 2N2 0 -* N2 02 " + N2 0 1.5 x 10

19 (dm6 mor2 s“2

) 72-9150

0- + N2 0^ (N2 O2 -)* 2.4 x 10

9 68-9071 c (N 2 02 ')^ NO' + no 2.5 x 10

6 68-9071 c NO' NO' + 2N2 0 N3 02 ' + N2 0 3.1 x 10

18 (dm6 mol~2 s

2

) 72-9150

NO- + N2 O ^ (N3 O2 -)* -» N3 O2 - 3 x 108 68-9071 c NO" + N2 0 -* N02 " + N 2 6 x 10

9 68-9071

NO' + N2 0 -* N2 0 + NO + e' 3.6 x 109 72-9150 c

a. The occurrence of this reaction is doubtful for ions of thermal energies (66-9042, 70-9229).

b. The reported formation of N02 may be due to O" + N02 —» N02 + O (66-9042).

c. Reaction assumed in the interpretation of the formation of ions observed in drift tubes.

TABLE 3.4. Ion neutralization reactions in irradiated N2 O (Pulsed irradiation at high

dose rate (1026 — 1028 eV g~ 1 s~

1 ) 72-0088)

Reaction G(reaction)/molecules (100 eV) 1

NO+ + e“ —* N(2 D) + 0(3 P) 0.73 NO+ + e

_ —> N(4 S) + 0(*D) 0.20 N2 0+ + e-->N2 (

1 2)+0(1 D) 1.20 N2 0

+ + e--^N2 (3 n)+0(3 P) 0.55 N2 0+ + e--^N(2 D)+N0 0 N2 0

+ + e-^N2 (3X)+0(3 P) 0.37

NOTE: These values were not measured directly but are derived from observed product

yield on the basis of several assumptions about the reaction mechanism. For a detailed discussion see reference 72-0088.

4. Product Yields Under Dosimeter Conditions

4.1. Nitrogen

N2 0 has been recommended as a gas—phase chemical dosimeter (56—0023). For this purpose,

N2 0 is irradiated at pressures in the region of 760 torr and room temperature (290 - 300 K).

Determination of N2 rather than any of the other products is recommended for dosimeter purposes

because the analysis of N2 presents no practical difficulties. Preferably, the total dose should not

exceed 1020 eV g

-1 (N2 0 conversion ca. 0.1 mol percent).

6
Reported absolute values of G(N2 ) for dose rates up to 1018 eV g

-1 s

-1 are given in table 4.1. (For

very high dose rate, pulsed irradiation see table 4.4).

Of the various methods of measurement of energy absorption, ionization-current measurement

is the most direct and capable of greatest accuracy (66-0434). The preferred value (table 4.1) is based on the most reliable determination using this method. For details of ionization chamber

design see 56—0024. For a discussion of the calculation of gas-phase dose from solution dosimetry

see 62—0146 and 63—0195.

Table 4.1. Initial G1 N2 )

1 Dose rates up to 1018 eV^s*1

)

G(N2 ) Source 10

15 Dose Rate

/eV g

_1 s

_1 10

20 Max. Dose' /eV g'1 Max. Conv. 1

/ mol percent N2 0

P(N2 0)

/torr T/K Dosimetry Anal. Ref.

11.5±0.4 a y 2.7 1.4 0.14 760 room F C,M 62-0146

12.8±0.4 b y 2.7 3.3 0.33 760 room I C,M 62-0146

10.7 ± 0.7 c y 10 2.7 0.3 760 287-295 F G 61-0103

9.9±0.8 d y 30 - - 250-1000 298 - C 63-0195

9.9 ± 0.5 y 2.1 0.27 0.02 660-1000 283 F C,G 69-0085

10.1 y 8.3 7.2 - 50-400 298 F C,G 70-0413

9.8* y 150 1.1 0.1 149 303 I C,M 65-0483

10.15* X (70 kV) 0.01 - - 200,555 room I c 58—0056

10.9± 1.0 X (4 MeV) 150 2.7 0.3 20-664 room C G 61-0103

10.0±0.2 g e~ (1 MeV) 102 - 103 1.0 0.1 200,600 297 I C,A 66-0434

11.3 ±0.5 /3~(T) 0.1 - 7 2.7 0.3 760 room s G 61-0103

10.0±0.4 a ( 210 Po) 2 0.43 0.04 440-680 298 s C,G 69-0085

10.6±0.5 h a (Rn) 0.2 2.4 0.2 100,200 303 I C 48-0003

Preferred value G(Nj) = 10.0 ± 0.2 Conditions: N2 0 pressure = 100 — 1000 torr Temperature = 290 - 300 K

NjO conversion 0.1 mol percent

Total dose ^ 1 x 10

20 eV g

_1

Dosimetry: F = Fricke dosimeter, C — Ceric sulphate dosimeter, I — Ionization current

determination, S = Radioisotope calibration Analysis: C = Trapping of condensables at 77 K. M = Mass spectrometry. G = Gas chromatography,

A = Combustion analysis.

a. G(Nj) from table 1 in paper.

b. High G(Nj) is attributable to incomplete ion collection in the ionization chamber used (see 66—0434).

Redesigned ionization chamber gave G(N2 ) = 10.0 ± 0.2 (G.R.A. Johnson and M. Simic, unpubbshed

results).

c. Values from table 1 in paper. Abnormally high G(N2 ) was observed in glass vessels with wall— to—wall distance less than about 1 cm. An opposite effect, i.e., low G(N2 ) in vessels packed with glass tubes, has been reported (66—0312).

d. Method of energy measurement not stated. Residual gas yield measured after trapping at 77 K but not analyzed. G(N2 ) given here is calculated assuming G(0 2 , after trapping) = 2.0 ±0.1 (see sec. 4.2).

e. Recalculated using 1F(N 2 0) = 32.9.

f. G(Nj) calculated from M/N = 4.0 reported for residual gas yield after trapping at 77 K, assuming 1F(N2 0) = 32.9 eV and G1 O2 . after trapping) = 2.0 ± 0.1. Author’s calculations, based on results with added

NO or 02 , gave G(N2 ) = 11.3.

g. Preferred value. Dose calculated using JF(NzO) =32.9 ±0.4 e\ 'ion pair)-1 (64-0177).

h. G(N2 ) calculated from M/N = 4.0 ± 0.2 given for the total yield of gases after trapping at 77 K, assuming

1F(N 2 0) = 32.9 and G(02 , residual) = 2.0.

i. Maximum dose and conversion at which the quoted G(N2 ) is stated to be valid.

4.2. Oxygen

The products from N2 0 radiolysis, other than N2 , are 02 , NO, and N02

. The possibility of chemical reaction between 02 and NO makes it difficult to decide whether NOz is a primary

product or is formed by secondary reactions between 02 and NO. This uncertainty complicates

the analysis of these products.

7

508-455 0 - 74 -2
For 02 determination, gas analysis, after trapping the condensable gases at 77 K, has usually

been employed (62—0146, 69—0085, 70—0413, 66—0434) but direct gas chromatography without

trapping has also been used (61—0103).

NO reacts with 02 relatively slowly at room temperature. On cooling to 77 K reactions (4) and

(5) occur, probably enhanced by mercury which is often present (58—0056).

2NO + 02 -> 2N02 (4) 4NO + 02 —» 2N2 03 (5)

Thawing, followed by refreezing, causes decomposition of N2 03 by reaction (6)

N2 03 ^N0 + N02 (6) so that the final stoichiometry of the reaction corresponds to reaction (4). The reaction of NO with

02 under the conditions used for gas chromatographic analysis is uncertain. It has been suggested

(61-0103) that the extent of reaction is negligible. However, evidence for quantitative occurrence

of a process of overall stoichiometry corresponding to reaction (5) has been obtained (71-7181).

4.2.1. Oxygen and Nitric Oxide Yields

In most determinations, the residual 02 yield, i.e., the 02 remaining, after trapping

condensable gases at 77 K, has been measured. There is reasonable agreement between

determinations of this quantity. The recommended value G(O2 , measured) = 2.0±0.2, selected

for the reasons given for the preferred G(N2 ). Table 4.2 gives reported values of the 02 yields. Values of G(02 ) have been calculated from

G(02 , measured). Where G(

2 , measured) is from the residual gas yield after condensing at 77 K,

G(02 ) was calculated assuming that the stoichiometry of the trap reaction is represented by

reaction (4) and that N02 and other nitrogen oxides are not formed directly as radiation products.

Table 4.2. Initial O2 yields (Dose rates up to 10lseVg~l s~l )

G(02 , meas.) G(02 ) Source 10

15 Dose Rate

/eV g

_1 s_1 10 20 Max. Dose

/eV g"1 p (N2 0)

/torr T/K Anal. Ref.

1.9 ±0.1 a,c 4.0±0.2 a,c y 2.7 1.4 760 room C,M 62-0146

2.6±0.2 b,c 3.8±0.3 b,c y 10 2.7 760 287-295 G 61-0103

1.8 ± 0.2 a,c 3.9±0.4 a,c y 2.1 0.27 660-1000 283 C,G 69-0085

1.4 a 3.8 d y 8.3 7.2 200 298 C,G 70-0413

2.5±0.3 b,c 3.8±0.4 b,c X (4 MeV) 150 2.7 20-664 room G 61-0103

2.0±0.2 a 4.0±0.4 a e” (1 MeV) 10

2 - 10

3 1.2 600 297 C,A 66-0434

3.2±0.2 b,c 4.1 ±0.3 b,c /r (T) 0.1 - 1.0 2.7 760 room G 61-0103

2.0±0.1 a 4.0±0.2 a a(

210 Po) 2 0.43 440-680 298 C,G 69-0085

Preferred values: G(02 , measured after trapping at 77 K) = 2.0 ± 0.2 G(02 ) = 4.0 ± 0.4 Conditions: N 2 0 pressure = 100 — 1000 torr Temperature = 290 - 300 K

N2 O conversion =£0.1 mol percent

Total Dose £ lx lO^eV g

_1

Analysis: C = Trapping of condensables at 77 K, M = Mass spectrometry, G = Gas chromatography,

A = Combustion analysis

a. G(Oz , measured) is the residual 02 yield after trapping at 77 K. G(02 ) is the calculated yield, assuming

that the trap reaction is 2NO + 02 —» 2N02

. b. G(0 2 , measured) is the 02 yield measured by direct gas chromatography of the irradiated gas. G(

2 ) is the calculated yield, assuming the reaction during analysis is 4NO + 02 —» 2N2 03

. c. Values corrected to G(N2 ) = 10.0.

d. G(02 ) was calculated by authors; basis of calculation not fully explained but presumably similar to that

in Note a.

8
Where G(02 , measured) is obtained by gas chromatography, it is assumed that reaction (5) occurs

during analysis (71—7181).

4.3. Nitric Oxide

Values for the NO yield, G(NO), can be obtained from the residual 02 yield after trapping at 77 K, G(02 , measured), assuming a stoichiometry for the trap reaction between NO and 02 (see

sec. 4.2). Addition of a small amount of NO before irradiation has also been used to determine

G(NO); in this case the total gas yield after trapping is 3/2 G(NO) + E(NO) where E(NO) is the

amount of NO added, assuming the trap reaction corresponds to reaction (4) (58-0056).

G(NO) has also been determined (61—0103, 62—0146, 66—0434) by extracting a known quantity

of the irradiated gas with aqueous sodium hydroxide solution in which the N03 ~ produced is measured by a spectrometric method. It is assumed that reaction (4) occurs rapidly in solution and

that NOj is formed according to reaction (7). 2N02 + 20H- -* N02 + NOj + H2 0 (7)

Table 4.3 summarizes values reported for NO yields. The preferred G(NO) = 4.0 ± 0.4 is selected on the basis of the preferred values for G(N2 ) and G(02 , measured) together with the

assumed stoichiometry of trap reactions. Directly measured values of G(NO) are in fair agreement

with this.

Table 4.3. Initial NO yield (dose rates up to 1018eVg~1 s *)

G (NO) Source 10

15 Dose Rate

/eV g'V1 10

20 Max. Dose

/eV g~l P(N2 0)

/torr T/K Ref.

3.7±0.3 a,b 7 2.7 1.4 760 room 62-0146

4.5±0.7 a,b,d y 10.0 2.7 760 288-295 61-0103

4.2±0.5 c,d y 2.1 0.27 660-1000 283 69-0085

5.1 b>c>e y 8.3 - 200 298 70-0413

4.5±0.6 b,c X(4 MeV) 150 2.7 390-660 room 61-0103

5.5±0.6 a,b P (T) 0 . 1 - 1.0 2.7 760 room 61-0103

4.0±0.2 C

<*( 210 Po) 2.0 0.43 440-680 298 69-0085

Preferred value: G(NO) = 4.0 ± 0.4 Temperature = 290 - 300 K

N2 O conversion =£0.1 mol percent

Total dose £ lx 1020eV g

_1

.

a. Analyzed as NOj after dissolving in aqueous NaOH.

b. Values corrected to G(N2 ) = 10.0.

c. Value from reported G(02 , measured) and G(N2

). d. Apparent G depended on vessel volume; this value is for vessel with largest volume.

e. G(NO) calculated from their results by authors; basis of calculation not explained.

4.4. Yields at Very High Dose Rate

The very high dose rates obtained with electron pulses from field emission tubes (S5 10 2 'eV

g

-1

s -1

) give initial product yields which differ from those at lower dose rates. Calorimetric

absolute dosimetry was used (68-0318, 71-0199) to obtain the values in table 4.4.

9
Table 4.4. Yields from very high dose rates (pulsed irradiation)

C(N2 ) 12.4 ±0.4 12.3 ±0.3

C(02 , measured) 2.5±0.3 —

C(02) 5.0±0.2 a C(NO) 5.0±0.2 a —

N2 O press/torr 380 - 760 ~ 900 - 2000

Temp/K 298-325 296 Dose rate/eV g

_1 s_1 1027b 2xl028c Total dose/eV g

_1 1.6 xlO20 5 x 1019 Dosimetry calorimetric calorimetric Reference 68-0318 71-0199

a. Yield measured after trapping at 77 K; G(02) calculated assuming 2N0 + 02 -* NO2 occurs as trap

reaction.

b. Delivered as electron pulse of half-height duration 30 ns (average electron energy 1 MeV, max.

current 5000 A).

c. Delivered as electron pulse of half-height duration of 3 ns, electron energy 600 keV, 200 A.

5. Effects of Conditions on Yields

5.1. Total Dose

Studies of the effect of total dose are few, but it is generally agreed that the G—values fall off as the total dose increases, presumably because of secondary radiolytic reactions involving the

accumulating radiation products. At sufficiently low doses the G values of the products are independent of dose (within an uncertainty of about 10%), but the maximum dose to which this

independence holds differs somewhat for different investigations, usually being between 1 and 3 x

1020 eV g

-1 (tables 4.1—4.3).

Reported values for the dependence of yield on dose obtained in deliberate studies of total dose effects are summarized in table 5.1.

Table 5.1. Dependence of yields on total dose

10'20 Dose

/eV g-‘ G(N2

)‘ G(02 meas'd.)b P(N2 0)

/torr T/K Dose rate /eV g-V*

Ref.

0.47 10.0 1.94 760 293 2. 7-5.0 x 10 1S 62-0146

1.00 10.0 1.87 760 293 2. 7-5.0 x 10

15 62-0146

1.20 10.0 1.72 760 293 2. 7-5.0 x 10 15 62-0146

1.30 10.5 — 760 293 2. 7-5.0 x 10 1S 62-0146

1.43 9.8 1.85 760 293 2. 7-5.0 x 10 15 62-0146

2.28 9.2 1.73 760 293 2. 7-5.0 x 10

15 62-0146

2.90 8.7 1.80 760 293 2. 7-5.0 x 10 15 62-0146

5.15 8.7 1.30 760 293 2. 7-5.0 x 10

15 62-0146

12.10 8.0 0.80 760 293 2. 7-5.0 x 10

15 62-0146

0.36 10.0 2.07 600 297 1.25-10.0 x 10

17 66-0434

0.59 10.0 1.82 600 297 1.25-10.0 x 10

17 66-0434

0.79 10.1 1.96 600 297 1.25-10.0 x 10

17 66-0434

0.74 10.1 2.13 600 297 1.25-10.0 x 10

17 66-0434

1.12 9.95 2.16 600 297 1.25-10.0 x 10

17 66-0434

1.20 9.76 2.04 600 297 1.25-10.0 x 10

17 66-0434

1.75 9.49 1.94 600 297 1.25-10.0 x 10

17 66-0434

0.1 10.0 — 1500 300 3 x 10

1S 60-0119

1.0 8.7 — 1500 300 3 x 1015 60-0119

10.0 7.6 — 1500 300 3 x 10

15 60-0119

100.0 6.65 — 1500 300 3 x 10

1S 60-0119

1000.0 5.7 — 1500 300 3 x 10

15 60-0119

a. Corrected assuming G(N2 ) = 10.0 at lowest total dose.

b. Residual 0 2 , after trapping at 77 K. 10
5.2. Pressure

Relatively little work has been aimed specifically at determining the effect of N2 0 pressure on

the yields. A survey of the values given in tables 4. 1-4.3 and summarized in table 5.2 suggests

that the initial G(N2 ), G(02 ),and G(NO) are independent of N2 0 pressure over the range 50 to 1000

torr N2 0, within an experimental uncertainly of about ± 5%.

Table 5.2. Effect of N2 O pressure on yields at room temperature

P(N2 0)

/torr G(N2 ) G(02 , measured) G(02 ) G(NO) Ref.

5 20.3 — — — 72-0449

10 16.2 0 5.0

d 12.

2

d 70-0384

21 10.9 2.5 3.8 — 61-0103

24.5 14.0 — — — 72-0449

47.5 12.1 —

— — 72-0449

50 9.5* 0.86* 3.45

d '* 5.2*’d 66-0434

50 14.4 — 3.95 13.1 58-0056

50 10.1 — — — 70-0413

100 10.6 — — — 48-0003

149 9.8 — — — 65-0483

200 10.15 — — — 58-0056

200 10.0 1.64 3.9d 4.5d 66-0434

200 10.6 — — — 48-0003

250b 9.9 — — — 63-0195

440b 10.0 2.0 4.0

d 4.0d 69-0085

555 10.15 — — — 58-0056

600 10.0 1.8 3.9

d 4.0d 66-0434

600 9.9 ! — — 69-0085

680 b 10.0 2.0 4.0

d 4.0

d 69-0085

760 11.5 1.9* 4.0

d 3.7* 62-0146

760 12.8 — — — 62-0146

760 10.7 2.6* 3.8

f 4.5* 61-0103

760 11.3 3.2* 4.1

f 5.5* 61-0103

1000b 9.9 — — — 63-0195

1000b 9.9 1.8 3.9 4.2 69-0085

8.8 x 10

3 11.

2

C 1.8 4.3 5.0 69-0085

1.54 x 104 11.

2

C 1.5 4.2 5.4 69-0085

4.4 x 10

4 10.

6

C 1.6 4.1 5.0 69-0085

1.32 x 10s 12.

l

c 1.6 4.4 5.6 69-0085

1.76 x 10s 12.

3

C 1.5 4.4 5.8 69-0085

2.42 x 10

s 13.

5

C 1.6 5.0 6.8 69-0085

3.08 x 10

s 11.

6

C 1.7 4.4 5.4 69-0085

a. Possibly not initial value.

b. Pressures quoted are upper and lower extremes of pressure-independent range.

c. Temperature = 311 K.

d. Calculated from residual yield after trapping at 77 K assuming trap reaction is 2NO + 02 —* 2NOz

. e. Corrected to G(N2 ) = 10.0.

f. Assuming 4NO + 02 —» 2N2 03 on gas chromatography.

g. Measured as N03 ~ in solution.

Above 1000 torr N2 0, the only investigation carried out (69—0085) suggests that there is little, if any, change in the product yields up to 3 x 105 torr N2 0.

Below 50 torr N2 0, there is evidence that G(-N2 0) increases and that the stoichiometry of the

radiolytic decomposition differs from that at higher pressures (58—0056, 70—0384, 70—0239). Not

all investigations found this effect of pressure (see 61—0103, 66—0434). It is possible that, in

addition to pressure, some other variables may be involved in determining the mechanism in the

low pressure region (e.g. temperature, surface or impurities). It has been shown (72—0449) that the

11
increased N2 0 decomposition at low pressures is eliminated by SF6 (2%) suggesting that the

electron is the primary species responsible. A chain reaction involving negative ions has been

proposed (72—0449; see sec. 3.3).

High decomposition yields obtained when N2 0 was irradiated with 200 kV x-rays (60-0107) were subsequently shown to be attributable to an electrical discharge induced by electrical fields

generated by the x-ray tube (62-0146).

5.3. Temperature

The effect of temperature on N2 0 radiolysis has not been systematically investigated at temperatures below 300 K. Reported yields indicate that there are no significant temperature

effects in the normal ambient range (283 - 300 K).

Increased decomposition with increasing temperature above 300 K was reported in early work

(19-0001) but relatively few studies of the effect of temperature have been carried out. The extent of thermal (non-radiolytic) decomposition of N2 0 apparently depends upon the

vessel surface. In stainless steel vessels, thermal decomposition becomes serious above 523 K

(66-0434). In glass vessels, thermal decomposition is not significant below 673 K (65—0483).

The available data (summarized in table 5.3.1) suggest that (1) the radiolytic decomposition is increased by increasing temperature, (2) the stoichiometry changes, favouring an increase in the

ratio G(NO)/G(02 ) at elevated temperatures, (3) the effect of temperature is more marked at low

N2 0 pressures, (4) the effect of temperature is less marked when very high dose—rate pulses are used.

Table 5.3.1. Dependence of yields on temperature

T/K G(N2 ) G(02 )‘ G(NO)* P(N2 0)

/torr

10 20 Max. dose

/eV g' 1 Dose rate /eV g'V1 Ref.

297 10.0 4.0 4.0 400 1.1 1.5 x 10

17 66-0434

343 12.4 4.5 7.0 400 1.1 1.5 x 10

17 66-0434

373 14.1 4.9 8.8 400 1.1 1.5 x 10

17 66-0434

423 17.9 6.1 12.2 400 1.1 1.5 x 10 17 66-0434

473 21.1 7.2 14.2 400 1.1 1.5 x 10

17 66-0434

303 10.0b — — 800 2.2 3 x 10

15 69-0534

373 b

er — — 800 2.2 3 x 1015 69-0534

473 23.

b — — 800 2.2 1.5 x 1017 66-0434

313 M bo

r-H 3.2*’c 7.0

C 50 1.1 3 x 1015 69-0534

356 12.

b 3.1 11.5 50 1.1 1.5 x 1017 65-0483d 423 25.

b 4.4 33.0 50 1.1 1.5 x 1017 65-0483d 523 48.

b 4.9 76.7 50 1.1 1.5 x 1017 65-0483d 583 61.

b 5.5 100.0 50 1.1 1.5 x 1017 65-0483d,e 646 78.

b 7.2 128.5 50 1.1 1.5 x 1017 65-0483de

a. Values calculated from residual yield of 02 or NO after trapping at 77 K assuming 2NO + 02 —> 2N02

. b. Values corrected assuming G(N2 ) = 10.0 at lowest temperature used.

c. Values calculated assuming reported residual yield of 02 is due to incomplete trap reaction.

d.

15 n14 no was used in this work. The values given are the sums of the various isotopically labelled species.

e. Glass vessels used, in which thermal decomposition is negligible below 673 K (65—0483).

In one investigation (65—0483, see table 5.3.2) the isotopic distribution in the products from

15 N14 NO was determined as a function of temperature.

With very high dose rate pulsed irradiation, the yields are independent of temperature up to 473 K (69-0013, table 5.3.3).

Since an increased decomposition of N2 0 with increasing temperature is not observed in the

presence of SF6 (69-0534) it appears that electron attachment is the primary process responsible

12
Table 5.3.2. Isotopic distribution in products from 15 N14 NO at different temperatures

28 N2 /% 7.8 15.0 10.0 10.3 9.6 10.7

29n2/% 83.5 76.7 84.3 86.4 88.0 87.3

30n2/% 8.7 8.3 5.7 3.3 2.4 2.0

,4 NO1% 68 65 60 56 54 54

15 NO/% 32 35 40 44 46 46 Temperature/K 313 356 423 523 583 646

Reference = 65-0483 Pressure N2 0 = 50 torr

for the temperature effect. Recently it has been suggested (72—0449) that electron detachment

from NO- (sec. 3.3) is more probable as a chain propagation step than the alternative suggested

reaction: NO- + N2 0 —» NO + N2 + 0~ (65—0483).

Table 5.3.3. Dependence of yields on temperature ( high dose rate pulsed irradiation)

G(N2 )* 12.4 12.4 12.4 12.4 13.8 13.8 15.3 16.5 22.0 27.5 G(02 , measured; 2.0 2.0 2.0 2.0 1.5 0.7 0 0 0 0 T/K 298 323 398 473 540 573 623 673 723 773 Values from 69-0013, fig. 1 N2 0 pressure = 760 torr Total dose 0.6 - 4 x lO^eV g

-1 Dose rate = 10

27 eV g

_1 s_1

a. Values at temperature above 573 K were corrected for thermal decomposition of N2 0.

b. Yield measured as residual gas after trapping at 77 K.

5.4. Electric Fields

The influence of D.C. electric fields on the course of N2 0 radiolysis was studied in early work

(see 48-0003 for references) and the application of this technique has been discussed in general

terms (54-0009). Although its interpretation is rarely unambiguous, knowledge of how electric

fields affect products can provide some information about the role of ion neutralization, of electron

capture and of excitation by slow electrons in a radiolysis mechanism.

For a dose rate 1013 eV g

-1 s

_1 and with 200 or 550 torr N2O, G(N2) and G(NO) increase with an

increase in the ratio, applied field/N2 0 pressure (X/P) in the region 1 to 7 V cm-1 torr

-1

, i.e., where

the ionization current is independent of X/P. A levelling off in the yields at about X/P =5 was

also reported although this effect is not apparent from the published results (58—0056). At 50 torr N2 0, G(N2 ) and G(NO) decreased as X/P increased, the values passing through a minimum at X/P

corresponding to the beginning of the plateau current region. At X/P higher than this, G(N2 ) and

G(NO) increased with increasing X/P, in a manner similar to that at higher pressures. At all pressures studied, G(02 ) showed only a slight increase with X/P in the region where secondary

ionization was negligible.

At a higher dose rate of 1017 eV g

-1 s

-1 also, G(N2 ) and G(NO) increased with X/P (66—0434). The

onset of the increase was the same for all N2 0 pressures between 50 and 500 torr and occurred in

the X/P region below that at which the ionization—current plateau was reached. The increase in

yields with X/P continued throughout the plateau region, the extent of the increase being greater

the lower the pressure. G(02 ) increased with X/P, but the increase was relatively small compared

with that for the other products over most of the ionization current plateau region.

The results at the higher dose rate therefore show a qualitative resemblance in that G(N2 ) and

G(NO) increase more markedly than G(02 ) at low X/P. The minimum in the N2 and NO yields

found at the low dose rates was not apparent at the higher dose rates.

13
6. Effects of Additives on Yields

Although mechanistic information can often be obtained by the use of scavengers, in the case

of N2 0, because of the large number of possible reactive intermediates and the rather poor

understanding of how these react with particular additives, it is difficult to select specific

scavengers. Relatively few scavenger studies have been reported and in no case has the

investigation been detailed.

Tables 6.1 and 6.2 summarize the limited information available.

Table 6.1. Limiting yields with various additives (y4) at room temperature

A Cone, of A

/ mol percent

G(N2 ) G(02 ) G(NO) P(N2 0)

/torr Ref.

CC14 0.4 6.7 ± 0.7 1.2(0.12)* — 800 69-0085

C02 7.5 9.4 ± 0.6* 2.1 ± 0.3* - 800 69-0085

co2 3-8* 7.5 ± 0.7 3.0 ± 0.2

d 3.5 ± 0.5

d 200 70-0413

NO* 0.25-8 10 ± T - - 50 65-0483

h2 1-16 10.0

f 2.3(l)b,h

i 90, 380 61-0103

h2 1-16 10.0* 0.13(16)

bb

i 90, 380 61-0103 c 2 h4 2.3 7.75,J - - 50 65-0483

ch4 6 10.0

f 0

h - 380 61-0103

sf6 0.1-1.

6.7*'m - - 800 69-0534

SF6 0.12-1.0 7.25 ± 0.6 1.8 ± 0.5* - 800 69-0085

sf6 0.01-0.2 8.0 3.2

d 3.1d 200 70-0413

sf6 0.3-5 1 8.2 ± 0.3

k - - 700 69-0369

Yields in absence of additives (cf. tables 4. 1-4.3): G(N2 ) = 10.0 G(02 , measured) = 2.0 (residual yield after trapping at 77 K). G(02 ) = 4.0

a. Residual O2 after trapping at 77 K.

b. G dependent on additive concentration; values are for the extremes of the scavenger concentration used, these being given in parentheses (mol percent).

c. Compare G(N2 ) = 9.9 ± 0.5 obtained in the absence of scavenger.

d. Yields are those calculated by the author from the residual yield after trapping at 77 K and were

corrected for the contribution from the energy absorbed by the scavenger.

e. Below 3 mol percent C02 , the G-values of the products increased with decreasing C02 concentration.

f. Calculated assuming G(N2 ) = 10 in the absence of scavenger.

g.

ls NO used as scavenger in uNuNO and 15 N

MNO. Given G(N2 ) is total N2

. For yields of isotopically labelled products see table 6.2.

h. Given values measured by direct gas chromatography of products.

i. G(NO, measured) decreased with increasing H2 concentration but appeared to reach a limiting value of

1.3 at H2 concentration greater than 5 mol percent.

j. G(N2 ) increased with temperature to 10.9 and 23.9 at 423 and 548 K respectively.

k. Very high dose rate (1027eV g

-1

s -1

) pulsed irradiation.

l. G(N2 ) increased with decreasing SF6 below ca. 0.3 mol percent. m. With 0.1 mol percent SF6 present G(N2 ) was essentially independent of temperature up to 473 K.

Table 6.2. Isotopically labelled products from N2 0 with 15 NO present (65-0483)

G(N2 ) 10 11.16 10.55 10 9.96 10.0 10.5 G(28 N2 ) 10 10.6 8.4 0.78 1.14 1.56 2.0 G(29N2 ) — 0.16 1.8 8.35 8.1 8.0 8.0 G(30 N2 ) — 0.4 0.35 0.87 0.72 0.55 0.48 G(14 NO) 2.15 7.6 — — — — - n2 o 14 N14 NO 14 N

14 NO 14 N14 NO 15 N14 NO 15N14NO 15 N14 NO 15 N

14 NO

15 NO cone. 0 0.25 5.7 0 1.6 7.9 26.0 (mol percent)

Values corrected assuming G(N2 ) = 10.0 in absence of NO.

14
7. Rare Gas Sensitized Radiolysis

Only one study of the yields from rare gas — N2 0 mixtures has been reported (70—0413).

Products were formed from N2 0 as a consequence of energy absorption in the rare gas fraction of

the mixture.

Difficulties arise in quantitative assessment of the data from this type of experiment since determination of the yield due to the energy absorbed by the rare gas, ^(product, sensitized), requires

knowledge of (a) the partition of total absorbed energy between the components of the mixture and

(b) the effect of the rare gas on the yield due to the energy absorbed by the N2 O fraction of the mixture, ^(product, N2 O). In the work reported (70—0413) it was assumed that the fraction of the total energy absorbed

by each component was equal to its electron fraction in the mixture (see 68—8036 for discussion of

the validity of the assumption). Results obtained with constant N2 0 pressure and varying rare gas

pressure indicated that G(product, N2 0) in the mixtures was the same as in pure N2 0.

Values obtained for G(product, sensitized) are given in table 7. These should be regarded as

tentative in view of the assumptions made in their calculation.

Table 7. Rare gas sensitized radiolysis of N2 O (70-0413)

G(N2 ) 7.3 6.3 3.0 2.9 3.8 G(02 ) 2.8 2.4 1.5 1.6 1.8 G(NO) 3.0 3.2 0.0 0.5 0.5 G(-Nz O) 8.8 7.9 3.0 3.2 4.1 Sensitizing Gas He Ne Ar Kr Xe

Reported yields are those attributable to energy absorbed in the rare gas fraction of the mixture. It is assumed that energy partition in gas mixtures is according to electron

density. G values obtained from slope of plot of (total yield of product/energy absorbed

by N2 0 fraction) against the ratio of the partial pressures P(rare gas)/P(N2 0). Those

plots were Unear (for mixtures with constant P(N2 O)=50 torr) for all products using He

and Ne, for all products except NO using Kr and Ar. Linearity was not observed for any

of the products using Xe. G(02 ) and G(NO) calculated from residual gas yield after trapping at 77 K, assuming

2NO+ 02 —» 2N02 .

8. N2 0 as Additive

One of the main uses of N2 0 in radiation chemistry has been as a selective scavenger for

electrons. In the gas phase, N2 0 was first used for this purpose in studies of hydrocarbon

radiolysis (65-0431). When it is present at scavenger concentrations, the radiation chemistry of

N2 0 is simplified compared with that of pure N2 0, and studies of N2 0 can give information about

some of its reactions, particularly electron capture and the subsequent negative ion reactions.

Information relevant to N2 0 radiolysis obtained in studies involving N2 0 as scavenger is summarized in tables 8.1 and 8.2. The effects of N2 0 on the products from the system are not

included. G(N2 ) is the yield due to energy absorption by the main components of the system.

Except where stated, G(N2 ) is independent of N2 0 concentration above the given N2 0

concentration. The "second additive" column lists compounds added to the main system to investigate their effect on G(N2 ). Some information about such effects is given in the comments;

for full details the references should be consulted.

15
Table 8.1. G(N2) from gases containing N2O as additive (organic systems)

System G(N2 ) Cone. N2 0

/mol percent

Other

Additives

10 ls -Dose Rate /eV g-V1 10

19 -Max.

Total Dose

/eV g

_1

Ref. Note

ethane 6.5 2 C02 , SF6 , alkenes 16 16 67-0247 a propane 7.2 2 SF6 , CC14 , C 3 H6 5.0 3.0 65-0431 a propane 6.5 2 alcohols 16 16 68-0005 a,b propane 6.5 2 h2 o, nh3 , chci3 10 3.0 69-0294 c butane 6.5 2 C02 , SF6 , alkenes 8.3 8.3 67-0247 a butane 6.5 2 alcohols 8.3 8.3 68-0005 a,b

iso-butane 6.5 2 alcohols 8.3 8.3 68-0005 a,b

propylene 4.2 2 — 11 1.1 68-0005 a iso— butylene 4.2 2 — 8.3 8.3 68-0005 a ciS-2-butene 8.4 2 co2 8.3 8.3 68-0005 a frans-2-butene 8.4 2 sf6 8.3 8.3 68-0005 a cyclohexane 11.5 2 sf6 8.2 2.2 68-0506 a benzene 13.3 10 — 34 4.5 68-0043 d benzene 24.9 3 sf6 , co2 4.1 9.1 68-0230 d methanol 48 6.5 — 0.38 9.0 65-0432 e methanol < 0.1 1 — 5 x 10® 0.5 64-0154 f

a. N2 formation attributed to dissociative electron capture by N2 O. Subsequent negative ion reactions are discussed.

b. Effect of MeOH, EtOH and 2—PrOH on secondary negative ions is discussed.

c. Temperature dependence of G(N2 ) studied. Effects of second additives attributed to negative ion clustering.

d. G(N2 ) dependent on N2 0 cone, and dose rate. Value given is the maximum observed. Chain mechanism involving 0~

suggested by authors.

e. Chain reaction indicated.

f. High dose—rate pulse irradiation.

TABLE 8. 2. G(N2) from gases containing N2O as additive ( inorganic systems)

System G(N2 ) N2 0

/ mol percent

Other

Additives

10

16 -Dose Rate

/eV g

- V1 10

19 -Max.

Total Dose

/eV g’ 1

Ref. Note

H2 0 3.8 > 0.1 — not stated 1.0 65-0005 a h2 o 3.5 3 SF6 , C3 H6 , C6 H6 0.5 3.0 67-0093 b h2 o 3.0 3 — 3.0 12 68-0112

NH3 (+C 3 H8 ) 3.8 1.5 sf6 , c3 h8 1.4 6.0 68-0659 c mn2 2.9 1.4 — 1.7 6.0 65-0791 d

a. Dosimetry not stated.

b. Values corrected to G(N2 ) = 10 in N 2 0 dosimeter.

c. High G(N 2 ) in absence of C3 H8 indicated chain reaction leading to N2

. d. System irradiated was

30 N2 + MN2 0. G(28 N2 ) decreased with increasing N2 0 concentration. Given value is extrapolated to zero N2 0 concentration.

I am grateful for the help of the staff of the Radiation Chemistry Data Center who assisted in

the preparation of this review. In particular, I am indebted to Dr. W.P. Helman and Dr. A.B.

Ross for their valuable advice and support. I thank Drs. D.A. Armstrong, P. Ausloos and L. Gevantman for their useful comments on the manuscript and Drs. C. Willis, A.W. Boyd and P.E.

Bindner for permission to include material from their work prior to publication.

16
9. References

19-0001 Chemical actions of radiation. Wourtzel, E. LE RADIUM 11: 289-98 and 332-47 (1919). 48-0003 The effect of electric fields on the decomposition of nitrous oxide by alpha—rays. Williams, N.T.; Essex, H.

J. CHEM. PHYS. 16(12): 1153-7 (1948).

53—

9004 Absorption coefficients of gases in the vacuum

ultraviolet. Part II. Nitrous oxide.

Zelikoff, M.; Watanabe, K.; Inn, E.C.Y.

J. CHEM. PHYS. 21(10): 1642-7 (1953).

54-

0009 The mechanism of gas phase radiation—chemical

reactions. Essex, H.

J. PHYS. CHEM. 58(1): 42-9 (1954). 56—0023 Nitrous oxide dosimeter for high levels of betas,

gammas, and thermal neutrons. Harteck, P.; Dondes, S. NUCLEONICS 14(3): 66-72 (1956).

56-

0024 Ionization chambers.

Boag, J.W.

Radiation Dosimetry, Hine, G.J. and Brownell, G.L.

(eds.). Academic Press, New York, 1956, p. 153-212.

57-

7006 Rate constants at low concentrations. III. Atomic

oxygen reactions in the photolysis of nitrogen dioxide

at 3600 A. Ford, H.W.; Endow, N.

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57-

9008 Reactions of nitrogen atoms. I. Oxygen and oxides of nitrogen.

Kistiakowsky, G.B.; Volpi, G.G.

J. CHEM. PHYS. 27(5): 1141-9 (1957).

58—

0056 The x-ray decomposition of nitrous oxide.

Burtt, B.P.; Kircher, J.F. RADIATION RES. 9: 1-12 (1958). 60-0107 A radiation-induced chain reaction in the decomposition of nitrous oxide. Johnson, G.R.A. PROC. CHEM. SOC.: 213-4 (1960).

60—

0119 Gamma irradiation experiments in the N2—O2 system.

Report No. 1 on radiation processing.

Steinberg, M.

BNL-612, June, 1960, 20p.

61—

0103 Nitrous oxide as a dosimeter for ionizing radiations. Heame, J.A.; Hummel, R.W.

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

62—

0146 The nitrous oxide radiation dosimeter. Johnson, G.R.A.

J. INORG. NUCL. CHEM. 24: 461-8 (1962).

62-

9017 Bond Energies, Ionization Potentials and Electron

Affinities. Vedeneyev, V.I.; Gurvich, L.V.; Kondrat'yev, V.N.; Medvedev, V.A.; Frankevich, Ye.L.

St. Martin's Press, New York, 1966, 202p.

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0195 High-dose N2 0 dosimeter.

Flory, D.A. NUCLEONICS 21(12): 50-4 (1963).

64-

0154 Production of hydrogen in the radiolysis of methanol

vapour. Meabum, G.M.; Mellows, F.W.; Reiffsteck, A. NATURE (LONDON) 204: 1301-2 (1964).

64-0177 Gas-phase dosimetry by use of ionization measurements.

Meisels, G.G.

J. CHEM. PHYS. 41(1): 51-6 (1964). 64-7008 Vacuum ultraviolet photochemistry.

McNesby, J.H.; Okabe, H. ADVAN. PHOTOCHEM. 3: 157-240 (1964). 64-9020 Negative-ion-molecule reactions in nitrous oxide. Burtt, B.P.; Henis, J.

J. CHEM. PHYS. 41(5): 1510-1 (1964).

64—

9021 Mass-spectrometric study of the reactions of O atoms

with NO and N02

. Klein, F.S.; Herron, J.T.

J. CHEM. PHYS. 41(5): 1285-90 (1964). Erratum: J. CHEM. PHYS. 44: 3645-6 (1966).

65—

0005 Electron yield in the y-radiolysis of water vapor. Baxendale, J.H.; Gilbert, G.P. SCIENCE 147: 1571 (1965). 65-0431 Effect of electron scavengers on the formation of hydrogen in the radiolysis of propane. Johnson, G.R.A.; Warman, J.M. TRANS. FARADAY SOC. 61: 1709-14 (1965). 65—0432 Effect of hydrogen atom and electron scavengers on

the radiolysis of methanol vapour. Meabum, M.; Mellows, F.W. TRANS. FARADAY SOC. 61: 1701-8 (1965). 65-0483 Radiolysis of N15 N14 0. Gordon, R.; Ausloos, P.

J. RES. NAT. BUR. STD. 69A: 79-85 (1965).

65-

0791 Isotopic exchange in nitrogen gas induced by y—

radiation. Dawes, D.H.; Back, R.A.

J. PHYS. CHEM. 69(7): 2385-92 (1965).

66—

0312 A practical comparison between nitrous oxide dosimetry and Fricke dosimetry for the estimation of y—ray energy absorbed in gaseous media.

Furukawa, K.; Shida, S.

J. NUCL. SCI. TECHNOL. (TOKYO) 3(1): 41-2 (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—9042 Some negative ion reactions in simple gases. Paulson, J.F. ADVAN. CHEM. SER. 58: 28-43 (1966).

66—

9163 Compilation of Mass Spectral Data. Cornu, A.; Massot, R. Heyden and Son Ltd., London, 1966, 323p.

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(4): 1118-23 (1967). 67—0247 Electron capture by nitrous oxide in irradiated alkane and alkene gases. Subsequent reactions of the O

ion. Warman, J.M.

J. PHYS. CHEM. 71(12): 4066-72 (1967). 67-9124 N2 O bond dissociation energy. Kaufman, F.

J. CHEM. PHYS. 46(6): 2449 (1967). 67-9126 Reactions of nitrogen atoms in the gas phase.

17
Brocklehurst, B.; Jennings, K.R. PROG. REACTION KINETICS 4: 1-36 (1967). 67-9127 Kinetic behavior of N2 (A3S U +

) in active nitrogen.

Thrush, B.A.

J. CHEM. PHYS. 47(9): 3691 (1967). 67-

9129 Study of collision-induced phenomena with a Dempster mass spectrometer.

Harris, H.H.; Russell, M.E.

J. CHEM. PHYS. 47(7): 2270-5 (1967).

68-

0005 The reaction of O

- with alcohols in gas-phase

radiolysis.

Warman, J.M.

J. PHYS. CHEM. 72(1): 52-6 (1968). 68-0043 Gas-phase radiolysis of benzene. Hentz, R.R., Rzad, S.J.

J. PHYS. CHEM. 72(3): 1027-31 (1968). 68-0112 Effects of electron scavengers in the radiolysis of water vapor. Dixon, R.S.; Bailey, M.G.

CAN. J. CHEM. 46(8): 1181-6 (1968). 68 -0230 The formation of phenol and nitrogen by a negative

ion-molecule chain reaction on irradiation of gaseous benzene—nitrous oxide mixtures. Rzad, S.J.; Warman, J.M.

J. PHYS. CHEM. 72(8): 3013-7 (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). 68-0506 y-Radiolysis of cyclohexane with electron scavengers.

VI. NjO and SF6 as electron scavengers in the vapor

phase.

Sagert, N.H.; Robinson, R.W.; Blair, A.S. CAN. J. CHEM. 46(22): 3511-6 (1968). 68-0659 Primary processes in the radiolysis of gaseous ammonia.

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

ADVAN. CHEM. SER. 82: 197-211 (1968). 68-7198 Vacuum-ultraviolet photolysis of N2 O. I. Metastable

species produced at 1470 A. Young, R.A.; Black, G.; Slanger, T.G.

J. CHEM. PHYS. 49(11): 4769-76 (1968). 68-8036 Energy deposition mechanisms.

Klots, C.E. Fundamental Processes in Radiation Chemistry,

Ausloos, P.(ed.), Interscience Publishers, New York,

1968, p.1-57.

68-9042 Three-body electron capture by nitrous oxide. Warman, J.M.; Fessenden, R.W.

J. CHEM. PHYS. 49(10): 4718-9 (1968). 68-9063 Gas phase reaction kinetics of neutral oxygen species.

Johnston, H.S. NSRDS-NBS-20, Sept., 1968, 49p.

68-9071 Negative-ion-molecule reactions in N2 O.

Moruzzi, J.L.; Dakin, J.T.

J. CHEM. PHYS. 49(11): 5000-6 (1968).

68-

9078 Electron attachment in N2 O. Phelps, A.V.; Voshall, R.E.

J. CHEM. PHYS. 49 (7): 3246-8 (1968).

69-

0013 Effect of temperature on yields in the radiolysis of nitrous oxide with high intensity electron pulses.

Boyd, A.W.; Willis, C.; Miller, O.A. CAN. J. CHEM. 47(2): 351-2 (1968).

69—0085 Effect of density and electron scavengers in nitrous oxide radiolysis.

Sears, J.T.

J. PHYS. CHEM. 73(4): 1143-46 (1969). 69-0294 Effect of polar molecules on reaction of negative ions

in radiolysis of hydrocarbon + nitrous oxide systems

in the gas phase.

Redpath, J.L.; Simic, M.

J. PHYS. CHEM. 73(9): 2809-14 (1969). 69-0369 Gas phase radiolysis of hydrogen chloride, hydrogen

bromide, and nitrous oxide with intense electron

pulses.

Willis, C.; Boyd, A.W.; Armstrong, D.A. CAN. J. CHEM. 47: 3783-91 (1969). 69—0534 Ionic processes in the radiolysis of nitrous oxide. Hummel, R.W.

CHEM. COMMUN. (17): 995-6 (1969). 69-6025 Vacuum-ultraviolet photolysis of N2 O. IV. Deactivation of N(2 D). Black, G.; Slanger, T.G.; St. John, G.A.; Young, R.A.

J. CHEM. PHYS. 51(1): 116-21 (1969) 69-7003 Vacuum-ultraviolet photolysis of N2 0. II. Deactivation

of N2 (A3 Xu +

) and N2 (B

3 nt

). Young, R.A.; Black, G.; Slanger, T.G.

J. CHEM. PHYS. 50(1): 303-8 (1969). 69-9031 Electron attachment to N2 0. Chaney, E.L.; Christophorou, L.G.

J. CHEM. PHYS. 51(3): 883-92 (1969). 69—9080 Critical evaluation of rate data fpr homogeneous, gas phase reactions of interest in high—temperature

systems.

Baulch, D.L.; Drysdale, D.D.; Home, D.G.; Lloyd, A.C. High Temperature Reaction Rate Data, No. 4, Dec.,

1969, 63p.

69-9129 Temperature dependence of dissociative attachment in n2 o

+

. Chantry, P.J.

J. CHEM. PHYS. 51(8): 3369-79 (1969). 69-9135 Negative ion-molecule reactions. Ferguson, E.E. CAN. J. CHEM. 47: 1815-20 (1969).

69-

9136 Negative ions of N2 O and CO2 . Bardsley, J.N.

J. CHEM. PHYS. 51(8): 3384-9 (1969).

70-

0046 Ion neutralization reactions in irradiated hydrogen

chloride, hydrogen bromide, and nitrous oxide. Wilson, D.E.; Armstrong, D.A. CAN. J. CHEM. 48(4): 598-602 (1970). 70-0239 The radiolysis of alcohols. Freeman, G.R. ACTIONS CHIM. BIOL. RADIATIONS 14: 73-134 (1970). 70-0384 Low pressure radiolysis of N2 O.

Bakale, G.; Fessenden, R.W.; Warman, J.M.

160th Meeting of the Am. Chem. Soc., Div. Phys.

Chem., Chicago, 111., Sept. 14-8, 1970, Abstr. No.

123. 70-0413 Ionic processes in the radiolysis of nitrous oxide. The

effect of electron scavenger and rare gas

sensitization. Takao, S.; Shida, S. BULL. CHEM. SOC. JAPAN 43(9): 2766-71 (1970). 70-7558 Reaction of 0(! D) with N2 O. Greenberg, R.I.; Heicklen, J. INT. J. CHEM. KINETICS 2: 185-9 (1970). 70-9074 Ion Molecule Reactions.

18
McDaniel, E.W.; Cermak, V.; Dalgarno, A.; Ferguson, E.E.; Friedman, L. Wiley—Interscience, New York, 1970, 374p.

70-

9229 Negative-ion-neutral reactions in N2 O. Paulson, J.F.

J. CHEM. PHYS. 52(2): 959-62 (1970).

71-

0199 The absolute dosimetry of high intensity 600 kV

pulsed electron accelerator used for radiation chemistry studies of gaseous samples.

Willis, C.; Boyd, A.W.; Miller, O.A. RADIAT. RES. 46: 428-43 (1971). 71-7181 The photolysis of N2 O at 1470 A. Dodge, M.C.; Heicklen, J. INT. J. CHEM. KINET. 3(3): 269-82 (1971). 71-7213 The reaction of the electronically excited oxygen atom

0(

1 D2 ) with nitrous oxide.

Scott, P.M.; Preston, K.F.; Andersen, R.J.; Quick, L.M. CAN. J. CHEM. 49(11): 1808-17 (1971).

71-

9364 Threshold electron impact excitation spectra. IV. Triatomic molecules nitrous oxide, carbon dioxide,

carbonyl sulfide, and carbon disulfide. Hubin-Franskin, M.J.; Collin, J.E. BULL. SOC. ROY. SCI. LIEGE 40(5-8): 361-84 (1971). 72-

0088 Primary yields and mechanisms in the radiolysis of N2 0 from high intensity electron pulse irradiations of N2 0-02 mixtures.

Willis, C.; Boyd, A.W.; Bindner, P.E. CAN. J. CHEM. 50(10): 1557-67 (1972) 72-0449 Dissociative attachment of thermal electrons to N2 O

and subsequent electron detachment.

Warman, J.M.; Fessenden, R.W.; Bakale, G.

J. CHEM. PHYS. 57(7): 2702-11 (1972). 72—9150 Electron attachment and negative ion molecule

reactions in nitrous oxide. Parkes, D.A.

J. CHEM. SOC. FARADAY TRANS. I 68(11): 2103-

20 (1972).

19

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Radiation Chemistry of Nitrous Oxide Gas.

Primary Processes, Elementary Reactions and Yields.

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ABSTRACT ( A 200-word or less factual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here.)

Data on the radiation yields from nitrous oxide gas, and the effects of

variables, including dose-rate, total dose, pressure, temperature, applied

fields and scavengers are reviewed and tabulated. The use of N20 as a gasphase, chemical dosimeter is discussed. Primary processes in irradiated

N2O are discussed and elementary reactions, relevant to the system, are

listed.

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KEY WORDS (Alphabetical order, separated by semicolons)

Chemical kinetics; data compilation; dosimetry; G; gas; nitrous oxide;

radiation chemistry; rates; review.

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