Geoscience Reference
In-Depth Information
where "
0
D
E
E
.c/
ˇ
ˇ
and F
.c
ˇ
are the energy and the absolute value of the
difference of forces at the crossing point of the ionic and dissociative terms). Then
the formula (Eq.
1.32
) may be rewritten as
(here E
.c/
2
2
R
e
V
ˇ
.2M
c
/
1=2
F
.c
ˇ
E
C
E
ˇ
!
v
0
1
=
2
X
v
1
E
v
0
!
:
.ˇ/
AI
D
v
0
D0
Replacing the summation over
v
0
by the integration, it is easy to obtain the known
semiclassical result (Smirnov
1981
):
;
ˇ
D
2V
ˇ
4R
e
ˇ
.2M
c
/
1=2
"
0
1=2
3F
.c
ˇ
E
C
E
ˇ
.
ˇ
/
AI
D
(1.34)
(the effective reaction threshold is equal to E
0
ˇ
D
E
ˇ
C
E
.c
ˇ
).
At the threshold of the new open channel
E
D
E
v
, the cross section (Eq.
1.32
)
shows a bend, the magnitude of which is characterized by the change in the cross-
section derivative d
AI
=dE in this point. The overall AI cross section behaves as
f.E/
E
C
E
ˇ
;
.ˇ/
AI
D
where f.E/is increasing monotonically as a result of the successive opening of the
new channels of the Rydberg XY
**
complex autoionization decay. From Eq.
1.32
it
is also implied that when
X
v
1
˛
ˇ
v
.
i
=/
˛
ˇ
v
0
;
v
0
a virtual population mechanism of the intermediate Rydberg states is dominant. The
formulae (
1.31
)and(
1.32
) refer to the case when the energy spread • of the atomic
beam exceeds the maximum interval E
v
1
<E<E
v
between the Rydberg levels
of the closed channels, i.e., ı>1
ı
v
. For the opposite case near the appearance
threshold of each newly opened up channel, generally speaking, a fine structure has
to be seen in the AI spectrum, namely in that part of it where ı
1
ı
v
.
At •
!
0 for the small Rydberg level widths
1
ı
3
, the AI cross section
can be written as (Golubkov and Ivanov
1988
)
h
˛
ˇ
v
0
"
v
0
C
˛
ˇ
v
0
C1
v
0
C1
i
;
v
1
4
2
R
e
V
ˇ
E
C
E
ˇ
X
.ˇ/
AI
D
(1.35)
v
0
D
0
