Environmental Engineering Reference
In-Depth Information
Figure 4.6
The Sena effect [40] in ion-atom scattering. As a result of the resonant charge ex-
change process, an incident atom becomes an ion, which leads to ion scattering, although inci-
dent particles move along straight trajectories.
Here the mobility expressed in square centimeters per volt per second is reduced
to the normal number density of atoms
N
a
10
19
cm
3
,theatompolar-
D
2.689
is measured in atomic units (
a
0
), and the ion-atom reduced mass
izability
α
μ
is
10
24
g). The accuracy of (4.88) may be found
from comparison of it with experimental data [21, 43-45] for the ion mobility in
gases, whose accuracy is up to 2%. Table 4.9 contains the experimental mobili-
ties of alkali metal ions in atomic and molecular gases [44, 46-50]. The ratios of
experimental mobilities for alkali metal ions in simple gases to those according
to (4.88) are given in Table 4.10 and characterize the accuracy of the Dalgarno for-
mula (4.88), which is estimated as 20%.
It is convenient to improve the Dalgarno formula (4.88) on the basis of these ex-
perimental data. The statistical treatment of experimental data allows one to reduce
the Dalgarno formula to the form [34]
given in atomic mass units (1.66
41
4
p
αμ
˙
K
D
,
(4.89)
Ta b l e 4 . 9
Experimental mobilities of positive alkali metal ions in gases. The mobilities are giv-
en in square centimeters per volt per second and are reduced to normal conditions (
N
a
D
2.689
10
19
cm
3
).
I , as e e r r e
2
N
2
O
2
Li
C
22.9
10.6
4.6
3.7
2.8
12.4
4.15
3.96
Na
C
22.8
8.2
3.1
2.2
1.7
12.2
2.85
1.63
K
C
21.5
7.4
2.7
1.83
1.35
13.1
2.53
2.73
Rb
C
20
6.5
2.3
1.45
1.0
13.0
2.28
2.40
Cs
C
18.3
6.0
2.1
1.3
0.91
12.9
2.2
2.27
