Geoscience Reference
In-Depth Information
The intermediate peaks are associated with the processes of the photo-ionization
and PINa
3
2
P
C
Na
.n;l/
!
Na
C
C
Na
C
e
with the participation of atoms in the
upper excited states populated by the
excitation energy transfer
(EET) processes.
At the same time, the position of the first electron peak
0.1 eV agrees well with
the idea that the autoionization decay of the quasi-molecular potential curve occurs
in the vicinity of the pseudo-crossing with the ion curve.
1.7
TheProcessesofaDoubleExcitation in the Binary
Collisions of Excited Atoms
The chain of interrelated collisional processes leading to ionization can be realized
when atoms are excited into the resonance states. One such example is the transfer of
energy primary excitation with the population of upper excited states, where almost
all the total internal energy is transferred to one of the partners (Eq.
1.60
). For the
first time, researchers have encountered the phenomenon of EET in experiments
with activated crystals, where the process of the excitation transfer occurs as a result
of the electron-phonon interaction, which is called a
cooperative luminescence
(Ovsiyankin and Feofilov
1968
).
The AI channel opens in experiments with the resonantly excited states of
the alkali atoms, which is accompanied by the heating of primary electrons and
the formation of the photo-plasma in the working volume. Thus, in addition
to EET the population of the upper atomic states by fast electrons should be
taken into account. Concentration of excited atoms and ionization value during
saturation of a resonance transition are both determined by vapor pressure. Studies
conducted to date of electrical kinetic parameters of the plasma sodium show
that the electron heating from the second kind of collisions in the sodium vapor
under saturation of a resonance transition starts from the density of normal atoms
N
0
D
2
10
13
cm
3
.
Inelastic thermal energy collisions can be considered as the transitions between
the terms of a quasi-molecule, corresponding to the initial and final states of the
colliding atoms. The EET processes occur in localized areas, concentrated in the
vicinity of the fixed values of the interatomic distance (see curves A
*
C
B
*
and
A
C
B
**
for
R
2
R
1
in Fig.
1.13
).
The total rate constant of these processes in binary collisions of the resonant
excited sodium atoms is 7
10
11
cm
3
s
1
. In the case of thermal collisions between
two resonantly excited sodium atoms, the EET processes have virtually no effect
on the efficiency of the AI reaction. Because the EET takes place at internuclear
distances where the covalent terms correlated as
R
!1
with the 2Na(3
2
P) states
are well known, calculation of the effective cross sections is possible in the theory
(Borodin and Komarov
1974
).
