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Fig. 1.9 Upper and lower ranges of values for the stress field of the discharge in nitrogen without
(curves 1 0 ,2 0 ) and with the addition of (curves 1, 2) a small admixture of mercury atoms
(2) the two-step ionization processes with the transfer of excitation energy,
A C A ! A C A;
(1.60)
and transition processes in the ionization continuum by the AI and PI, as well as the
formation of the ion pair
8
<
A 2 C e ;
.1:61/
A C A !
A C C A C e I
.1:62/
:
A C C A :
.1:63/
At the same time there is a wide range of conditions in which the collisional
processes involving atoms in the emitting states can give a significant contribution
to the ionization. Thus, an ensemble of the excited states formed in an absorbing
medium, irradiated by light, in general, is a potential source of the processes
leading to the ionization. For example, if the external light field is “weak” (for the
field strength E < 10 6 Vcm 1 ), and multiphoton excitation and ionization do not
occur, the population of excited alkali metal atoms resulting from absorption can be
induced by collisions.
Considering the ionization of the absorbing medium in the single-component
weak light fields with photon energy less than the ionization potential of the
atom, there are two primary ionization mechanisms: the photo-ionization of the
excited states and ionization in thermal collisions of atoms. Reactions of this
type occur in experimental facilities and in various plasma chemical devices in
 
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