Geoscience Reference
In-Depth Information
Tabl e 1. 1
Total chemoionization cross sections
t
D
AI
C
PI
and branching ratios of the
reactions
D
AI
=.
AI
C
PI
/ for the He(2
3
S)
He(2
3
S) and He(2
3
S)
He(2
1
S) collisions as
functions of kinetic energy
E
References
E
,10
3
t
(10
16
cm
2
)
eV
He(2
3
S) C He(2
3
S)
Muller et al. (
1991
) theory
1
318
0.09
33
106
0.032
60
92
0.023
Muller et al. (
1991
) experiment
1.6
--
0.07
˙
0.03
61
--
0.03
˙
0.03
Garrison et al. (
1973
) experiment
33
112
˙
30
0.046
˙
0.006
Garrison et al. (
1973
) experiment
33
135
˙
23
0.07
˙
0.04
Kolokolov and Kudryavtsev (
1989
) theory
33
0.07
˙
0.03
He(2
3
S)
He(2
1
S)
Muller et al. (
1991
) experiment
C
1.6
859
˙
255
0.14
˙
0.03
61
193
˙
92
0.08
˙
0.03
Devdariani et al. (
1983
) theory
33
0.16
˙
0.06
Fig. 1.8
Electron energy
distribution function under
the afterglow discharge
conditions (Adapted from
Bezuglov et al.
1994
)
f
f
distribution function. The electronic spectra correspond to two channels of the
chemo-ionization: (1) He(2
3
S)
C
He(2
3
S) and (2) He(2
3
S)
C
He(2
3
S). The shaded
region (in Fig.
1.8
) corresponds to the process of AI. A quantitative interpretation
of the spectrum allows us to draw the following conclusions. The share of AI
in the ionization of symmetrical collisions of 2
3
S atoms is 7%
˙
4%. For the
asymmetrical 2
3
S
2
1
S transition involving the formation of molecular ions in
high vibrational excited states, it is 16%
˙
6%. If the concentration of metastable
atoms considerably exceeds the plasma electron concentration, which is realized
with the fast decrease of the electron temperature T
e
in the afterglow plasma with
nonequilibrium recombination, increase of degree of ionization is observed after the
discharge current disappears.
A comparative analysis of theoretical and experimental spectra of plasma
electron spectroscopy allows us to estimate the dissociation energies of the
quasi-molecules He(2
3
S)
C
He(2
3
S) and He(2
3
S)
C
He(2
1
S), which are equal to
0.9
˙
0.2 eV and 0.6
˙
0.2 eV, respectively. The calculation of the rate constants of
