Geoscience Reference
In-Depth Information
Fig. 1.21
Cross section (
n
)
of near-threshold ionization
in Rydberg atom-Rydberg
atom collisions
The constants of the atomic ion formation in the binary collisions of Rb(11
2
P)
measured by Borodin et al. (
1995
) were compared with the results of the calculation
within the model approximations, which were used in two previous studies. The
measured value
k
D
(1.5
˙
0.4)
10
8
cm
3
s
1
within a factor of 2 coincided with
the calculated value.
Recently, interest in the processes has increased, such as PI reactions with
the participation of the Rydberg atoms, caused by the effects of the cold plasma
formation in the magneto-optical traps (Amthor et al.
2009
).
1.9
Formation of Negative Ions in Thermal Collisions
with Rydberg Atoms
1.9.1
Symmetrical Collisions
Let us discuss the possibility of negative ions in thermal collisions of the excited
and normal atoms of one kind.
Figure
1.22
shows the scheme of the terms of the excited molecule X
2
*
, ground
state molecule X
2
, and the potential curve of the Coulomb ion pair X
C
C
X
.We
assume that at large interatomic distances
R
the Coulomb interaction is the main.
The value of
R
c
, at which a pseudo-crossing of the covalent X
2
*
and the Coulomb
X
C
X
potential curves can be estimated from the approximate relationship
E
-
e
2
/
R
c
,where
E
is the energy defect of the reaction. From this it follows that the
formation of the pair X
C
C
X
can occur from the excited states of X
*
,forwhich
E
is of the order of
kT
a
. In real cases, the effectiveness of such a reaction is
determined not only by the value of
E
. Thus, it was shown that the preferential
population of the excited states with a zero-energy defect does not take place in the
