Environmental Engineering Reference
In-Depth Information
Ta b l e 2 . 5
Parameters of the resonant charge exchange at a collision energy of 1 eV in the lab-
oratory frame of reference. The parameter
γ
is given in atomic units, and the cross section of
resonant charge exchange
σ
res
is expressed in 10
15
cm
2
.
Element
γ
R
0
Element
γ
R
0
γ
σ
res
γ
σ
res
H
1.000
10
0.22
4.8 Mo
0.722
15
0.17
19
He
1.344
10
0.22
2.7
Pd
0.783
15
0.14
16
Li
0.630
14
0.16
22
Ag
0.746
15
0.16
17
Be
0.828
12
0.20
10
Cd
0.813
14
0.16
14
N
1.034
12
0.17
6.4
In
0.652
15
0.15
24
O
1.000
12
0.19
6.9
Sn
0.735
15
0.17
19
Ne
1.259
11
0.20
3.2
Xe
0.944
14
0.14
10
Na
0.615
15
0.17
26
Cs
0.535
17
0.15
44
Mg
0.750
14
0.18
15
Ba
0.619
16
0.15
30
Al
0.663
14
0.12
19
Ta
0.762
15
0.16
17
Ar
1.076
12
0.17
5.8 W
0.766
15
0.16
17
K
0.565
16
0.16
34
Re
0.761
15
0.16
17
Ca
0.670
14
0.18
15
Os
0.801
15
0.14
15
Cu
0.754
14
0.16
16
Ir
0.816
15
0.15
14
Zn
0.831
14
0.18
12
Pt
0.812
14
0.15
14
Ga
0.664
15
0.16
22
Au
0.823
15
0.16
14
Kr
1.014
13
0.16
7.5 Hg
0.876
14
0.15
12
Rb
0.554
16
0.15
38
Tl
0.670
15
0.16
22
Sr
0.647
15
0.16
25
Bi
0.732
16
0.14
22
Note that we are using the asymptotic theory of resonant charge exchange, which
is guided by the classical character of nuclear motion [55, 64]. It is valid at large
values of the collision momentum
l
res
:
D
μ
gR
0
„
l
res
1.
In particular, in the case of resonant charge exchange involving helium (He
C
C
He)
at a thermal collision energy
ε
D
0.026 eV we have
l
res
D
27, that is, the classical
criterion holds true.
It should be noted that the cross section of elastic ion-atom collision is less than
the cross section of resonant charge exchange if the collision energy exceeds the
thermal energy. Table 2.6 contains the ratio of the diffusion cross section (2.40)
of elastic ion-atom collision to the cross section of resonant charge exchange at
collision energy
mg
2
/2
0.1 eV, where
m
is the mass of the atom or ion and
g
is the relative velocity of colliding particles. The statistical treatment of these data
gives a value of 0.95
ε
D
D
0.14 for this ratio.
The cross section of resonant charge exchange depends weakly on the collision
velocity, whereas the elastic cross section of ion-atom scattering increases with
decreasing velocity. Hence, elastic ion-atom scattering becomes important at low
˙
