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of the elastic and inelastic scattering of slow electrons by molecular ions, the
dissociative recombination between electrons and molecular ions, and the associa-
tive ionization of atoms, as well as elastic and inelastic collisions between atoms
involving the dissociative states whose potential curves lie closely to the minimum
of the ion's potential energy (Golubkov and Ivanov 2001 ). Another important group
comprises the processes
e C XY C
XY C h ! XY
(photoionization and photodissociation) induced by the single- or multiphoton
absorption. The processes in question also include free-free radiative transitions,
such as the electron bremsstrahlung
e C XY C ! XY ! XY C C e C„
where is the bremsstrahlung frequency.
Processes ( 2.1 , 2.2 ,and 2.3 ) play a substantial role in gas discharge lasers,
low-temperature plasmas, and various atmospheric and astrophysical phenomena
(Stebbings and Danning 1983 ). The effects of external physical factors on their
dynamics are also of great interest. In particular, laser control of elementary atomic
and molecular processes is a fundamental problem in modern chemical physics. As
a tool for controlling these processes, the laser has a number of advantages over
classical light sources. First, a highly monochromatic laser beam can be used to
achieve the frequency selectivity required to obtain detailed information about a
quantum system, such as energy levels, their decay widths, and radiative lifetimes.
Second, varying the beam intensity and using a tunable laser, one can determine
these characteristics as functions of a laser field strength and frequency, respectively
(Ivanov and Golubkov 1991 ). Third, owing to the high intensities attainable, the
present-day laser technology provides tools for a direct control of gas-phase reaction
rate constants (Hirschfelder 1989 ).
Status of the Theory
Laser-atom interaction has been discussed in a vast literature (Delone et al. 1983 ;
Delone and Krainov 1978 ; Rapoport et al. 1978 ; Delone 1989 ; Lambropoulos
1976 ;Swain 1980 ; Rosenberg 1982 ; Mittleman 1982 ). The perturbation theory
generally describing the behavior of a molecular system interacting with an external
electromagnetic field is inapplicable when the field is strong. The concept of the
strong field is explained as follows. If the amplitude of the laser field strength f is
comparable with the atomic field strength f a ' 5:14 10 9 V=cm (which corresponds
to beam intensities of
10 17
W/cm 2 ), then the multiphoton ionization rearranges
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