Geoscience Reference
In-Depth Information
Chapter 1
Ionization of Excited Atoms in Thermal
Collisions
N.N. Bezuglov, Gennady V. Golubkov, and A.N. Klyucharev
Abstract
This topic is devoted to the modern theory and experimental inves-
tigations of the associative ionization (AI) reaction. The means of their further
development are analyzed. Numerous applications in plasma chemistry, aeronomy,
chemical physics of the upper atmosphere, and astrophysics have contributed to
conducting this study. The threshold behavior of cross sections of the endothermic
reaction AI is considered, and it is shown that the dependence of above-threshold
energy E is a strictly linear in the quantum case, which differs substantially from
the law
E
3/2
, resulting in a semiclassical theory. This result has a simple physical
explanation because the matrix elements of scattering operator resulting from the
tunneling effect are finite at
E
D
0. Comparison with the semiclassical theory
has been made. A substantiation of the described possibility of elementary AI
reaction dynamics in the diffusion approach is given. A detailed consideration of the
applicability conditions of the “quantum chaos” theory for the spectrum of highly
excited Rydberg molecules is carried out. A review of experimental studies of AI
reaction under different conditions covering vapor cells, single effusive beams, two
crossing beams, and cold matters (very briefly) is presented. The importance of
accounting for specific distribution functions of atoms over a relative (colliding)
velocity in AI rate constant evaluations is discussed, and a proper explanation of
noticeable variations in experimental data is provided. Different types of colliding
atomic/molecular pairs consisting of low-lying excited states (normal, metastable,
and resonance) in inert and alkali gases are considered, and the corresponding
futures of AI cross sections are analyzed. Experimental data on AI and Penning
ionization processes involving the Rydberg states of hydrogen and alkali atoms
