Geoscience Reference
In-Depth Information
Hg
6
3
P
1
C
Hg
6
3
P
1
!
Hg
C
2
C
e
(1.55)
Hg
6
3
P
1
C
Hg
6
3
P
0
!
Hg
C
2
C
e
(1.56)
Hg
6
3
P
0
C
Hg
6
3
P
0
!
Hg
C
2
C
e
(1.57)
Collisions of the second kind of the optically excited 6
3
P
1
hydrargyrum (helium)
atom and a molecule of nitrogen lead to the population of 6
3
P
0
metastable state
with a concentration three orders of magnitude greater than the population of the
emitting 6
3
P
1
level.
The rate constant of the process (Eq.
1.57
), which is the main ionization
channel under the experimental conditions, equals
k
D
(4.0
˙
0.8)
10
10
cm
3
s
1
at
T
D
295 K. It agrees with the calculation result obtained in the framework of the
polarization capture theory and allows us to treat this process as a zero-threshold
one (Klyucharev
1993
). For the case of the cadmium atom, the values of the chemo-
ionization constants obtained in the same way for the unit 5
3
P
0,1,2
-state value are
equal to 4
10
12
cm
3
s
1
at
T
D
575 K. The double excitation energy of the
6
3
P
0
state of the hydrargyrum (mercury) atom is 9.34 eV, which is higher than the
ionization potential of 10.43 eV of the normal atom, leading to the assumption of
the zero-threshold nature of the process and to an estimate of the molecular ion
dissociation energy equal to De
C
Hg
2
1 eV.
Change of the electrokinetic parameters of the gas discharge plasma and the
formation of the current-free plasma in the hydrargyrum vapor in the resonance
radiation are associated, for example, with the reaction (Eq.
1.57
)ofchemo-
ionization (Fig.
1.9
). The resulting free electrons may participate in the balance
of the level populations of the laser to mercury vapor.
Discussion of the literature data on the constants of chemoionization in thermal
collisions with metastable atoms shows that the rate constants of zero-threshold
reactions may be as high as 10
6
to 10
10
cm
3
s
1
.
1.6
Ionization in Collisions Between Atoms in the Resonant
Excited States
The sequence of related collisional processes leading to the effective ionization of
the medium can be realized when atoms are excited into a resonant state. Let us
consider the main types of the symmetrical collisions for this case, which include
(1) the chemoionization process in pair collisions of the excited atoms,
(
A
2
C
e ;
.1:58/
A
C
A
!
A
C
C
A
C
e
I
.1:59/
