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X *
X + +X
E a E i *
X * + X
U i (X)
X + +X
Illustration of the mechanism of X **
Fig. 1.22
X collision process
framework of the Landau-Zener transition mechanism as the result of the reverse
process of the ion-ion recombination. For the highly excited states, the crossing of
the covalent repulsive s term of the quasi-molecule and the Coulomb term of the
X C C X does not occur. Then, the formation of the positive and negative ions
can take place through the transitions such as the Rosen-Zener at small internuclear
distances, or with a help of a third covalent term, which correlates with the lower
excited states at R !1 . A formation of the negative ions in the system
Rb .nl/ C Rb 5 2 S ! Rb C C Rb
is considered at the temperature T a D 540 K by Barbier et al. ( 1986 ). The specificity
of the Rydberg atoms, which manifests itself in collisions with heavy particles, is
that the ionic cores and the valence electrons have different effects on the nature
of the collision. The ion core controls the diffusion of the Rydberg atoms in a gas.
Formation efficiency of the negative ions in collisions with heavy electronegative
particles is caused by the scattering of the outer electrons. The formation of the
negative ion Ca in the thermal collisions with the neon Rydberg atoms in ns and
nd states, in the range of 8 < n eff < 14, was investigated by Reicherts et al. ( 1997 ).
The dependence of k ( n eff ) has a maximum k max 10 8
s 1 at the point of
n eff D 11.5, which was not observed in this range for the pair Ne **
cm 3
C SF 6 .This
finding is in good agreement with the results of the model calculations of the calcium
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