ATOMIC•AND MOLECULAR PROCESSES IN THE GAS PHASE AS STUDIED BY
A PULSE RADIOLYSIS METHOD
Y. Hatano, K. Shinsaka, A. Yokoyama 1 >,· Y. Kokaku 2 >, N. S~zuki,
M. Toriumi, A. Nishikawa, and H. Koizumi
Department of .Chemistry, Tokyo Institute of Technology,
Meguro-ku, Tokyo.152.
1. Introduction
We have been studying the thermal electron attachment to anoxygen molecule by a pulse radiolysis~microwave cavity technique 3 >,and the de-excitation processes of excited rare gas atoms by time- ·resolved spectroscopy, using a relatively light versatile electron
pulse accelerator, Febetron 706. We report here some applicationof the accelerator by the recent results of our experiments on thethermal electron attachment in some o2 -hydrocarbon mixtures andthe de-excitation of excited rare gas atoms.
2. Thermal electron attachment in some o2-hydrocarbon mixtures
The sample gas was introduced into a cylindrical X-band
microwave cavity and was irradiated by a X-ray pulse from Febetron
706, Which produces a 600 keV electron beam pulse of triangulartime profile with a half width of several nanoseconds("-700 0 A).
The microwave circuit which is the Pound type frequency discriminator including two Magic Tees and two detector diodes was used
for the measurements. Differentially amplified signal between thediodes is accurately proportional to the shift of the cavity
resonant frequency, in .the result, to. electron concentration.
Thermal electron attachment to o2 in the presence of third
body molecule(M) at low 3 ~ressures has been explained by the Bloch·
Bradbury (B-B) mechanism :With increasing the pressure of M, the effective two body rateconstant of electron attachment, keft' continues to increase andexceeds the limiting value k1 which ~s expected by the B-B rnechar----.,....---.---..-- r---.---.--..--.
,....
nism as shown in Fig. 1.
~ 4
This excess part of eleckeff~tron attachment process
o2- •• ~·'
~
e+
02
~
has been ascribed toB3
electron attachment to~ ~van der Waals molecule~ ~ 2(02•M)4):......

.....

~(02•M) + eks~( k6(02•M) -* + M(02•M)'-*1Ik02- + 2M.
~The rate constant of theinitial electron attach-·ment to (02•M) is foundabout two orders of magnitude larger than thatfor 02 itself as given in
Table 1 (cf. k1 = (4.8 ± 0.6)
x 1o-11 cm3jsec)3,4).

023

PM (lQ19molecule/cm3)

Fig. 1. Effective rate constant for
02-C2H6 mixtures as a function ofdensity of C2H6· Solid curve shows
the contribution of the B-B .mechanism.
-275-

~~-~

---- - - - -Table 1. Initial electron
3. De-excitation of excited rareattachment rate constantgas atoms
3.1 Time-resolved optical absorption6-9) of excited neon atoms Ne(3P 1 , 3p 0 , 3p?,) has been measured
k5
after the irradiation of pulsedMelectron beam from Febetron 706 upon
(1o-11 cm3 s-1)
Ne-M mixtures. At high electron
densities the decay rates of neon 1s
800
C2H6states are affected by thermal
electrons as shown in our observa200
C3H 8tion of optical emission accompanying
2000
n-C4H1o
1s states(Ne*) from higher energystates(Ne**) through a dissociative
500
C2H4
recombination of Ne2+ with e-, andalso in the observation of collisional mixL1g between 1 s states :Ne2+ + ec" ~ Ne** + Ne, Ne**--+ Ne* + hv, Ne* + e- ~ Ne*' + e-.
The addition of a small afuount of SF6 was effective in suppressing
the effect due to thc,ecmal electrons. The obtained rate constantsfor Ne are given in Table 2 showing only two examples, due to thelimited space, of among twelve compounds examined.
3.2 Energy transfer from Ar(1P 1 , 3p 0 , 3p 1 , 3P2) to N2(C 3nu, v' =0, 1, 2, 3) has been also studied by measuring both the timeresolved optical absorption of each argon excited state(Ar*) andoptical emission of N2(C 3nu ~ B 3n ) • The effect of thermalelectrons was also removed by the ad~ition of a small amount of
SF6. Energy transfer rate constants from Ar* to N2 and SF6 weredetermined as in Table 3.
Table 3. Ar* de-excitation
Table 2. Ne*(3PJ) de-excitation
rate constants
rate constants and cross sections
MAr*k(1o-11cm3s-1)
MJk ( 1 o-1 Ocm3s-1)
c; {1\2)10.65 ± 0.05
0.67 ± 0.09
0.81 ± 0.06

8.6
8.9
11201

2.3 ± 0.2
3. 1 ± 0.2
4.2 ± 0.3

3852702lJ2SF601 p1
N23po
3p1

3p2
1 p1
3po
SF'63p1
3p2

5.8 ± 0.6
2.4 ± 0.4
3.9 ± 0.5
2.9 ± 0.2
98.9 ± 6.0
34.7 ± 0.7
61 . 9 ± L'"

33.0 ± 0.91)Present address:Japan Atomic Energy Research Institute,
Tokaimura,Ibaraki 319-11.
2)Present address:Prog.Eng.Res.Lab.,Hitachi,Totsuka-ku,
Yokohama 244.
3)H.Shimamori and Y.Hatano,Chem.Phys.Lett.,38,242(1976);Chem.
Phys., 12,439 (1976) ;Chem.Phys. ,21,187 (1977).4)Y.Kokaku,Y.Hatano,H.Shimamorl; and R.W.Fessenden,J.Chem.Phys.,
71,4883 (1979).
S)Y.Kokaku,M.Toriumi, and Y.Hatano,J.Chem.Phys.,to be published.
6)T.Ueno and Y.Hatano,Chem.Phys.Lett.,40,238(1976).
·
7)T.Ueno,A.Yokoyama,S.Takao, and Y.Hatano,Chem.Phys.,45,261 (1980).
8)A.Yokoyama,S.Takao,T.Uuno, and Y.Hatano,Chem.Phys.,45,439(1980).
9)A.Yokoyama and Y.Hatano,Chem.Phys.,to be published.---276-