Geoscience Reference

In-Depth Information

Fig. 1.3

The same as for Fig.
1.2
with a quasi-crossing of the potential curves in the point
R
c

Coulomb refinement levels) is solved in the special model case, then the set of

Rydberg terms is replaced by a system of the parallel lines, and the diabatic

dissociative term is also linearized. In the framework of the Demkov-Osherov

contour integral method (Demkov and Osherov
1968
), the problem is reduced to

multiplying the probabilities to stay on the dissociative term at each point of pseudo-

crossing (followed by a summation of the exponents of all these points). This

approach is reasonable if the ionization and the transitions to highly excited states

are determined by the behavior of the system near the avoided crossing
R
c
in the

small neighborhood
L
R
, which is the parameter of the problem. Upon reaching the

point,
R
D
R
c
of the bound state disappears, merging with a continuous spectrum.

The ionization cross section in this approximation is equal to R
c
.

In the 1970s, the majority of model theoretical studies of the AI process were

performed without a set of avoided crossings that occur right up to the potential

curve of the quasi-molecule across the border of the molecular ion continuum.

Attempts to take them into account in the framework of the traditional approaches

based on individual review of each pseudo-crossing for highly excited states

were not successful. In this regard, we developed a method that implements the

“diffusion-based approach to the collision ionization of excited atoms” (Devdariani

et al.
1988
). We are talking about the diffusion over the quasi-molecule state

energies in a single act of the collision: the main collision parameter is the binding

energy of the excited electron. During the “diffusion,” the initial single quasi-

molecule term is transformed into a “burning” type of conic section at large

distances (
R
!1
) with decrease in
R
(Fig.
1.4
).