Environmental Engineering Reference
In-Depth Information
where
K
0
is the mobility of an atomic ion in a parent gas in the absence of elastic
scattering,
x
is given by (2.47), and we account for a weak velocity dependence
of the cross section of resonant charge exchange [56]. We also take into account
in this formula the limiting case of low collision velocities. Table 4.12 gives the
contribution of elastic scattering at room temperature, and elastic scattering leads
to a mobility decrease.
As follows from the data in Table 4.12, because of elastic ion-atom scattering the
ion mobility in parent gases at room temperature decreases by approximately 10%.
Table 4.13 gives the experimental values of the ion mobilities for atomic ions of
inert gases in a parent gas at an indicated temperature. These values are averaged
over various measurements, and the indicated accuracy corresponds to statistical
averaging of experimental data. The zero-field mobilities of atomic ions of inert
gases in a parent gas at some temperatures evaluated on the basis of (4.93) and
(4.94) are given in Table 4.13 in parentheses.
As a demonstration of these results, we show in Figure 4.7 the temperature de-
pendence for the mobility of atomic helium ions in helium which includes (4.94)
for the mobility due to resonant charge exchange and accounting for elastic ion-
atom scattering as a correction, and experimental results [57-62].
Ta b l e 4 . 12
Relative variation
Δ
K
/
K
of the zero-field mobility of ions
A
C
in a parent gas
A
due
to elastic scattering at room temperature for inert gases and alkali metal vapors.
A
Δ
K
/
K
,%
A
Δ
K
/
K
,%
He
5.8
Li
12
Ne
7.8
Na
8.2
Ar
11
K
8.9
Kr
6.0
Rb
7.7
Xe
9.2
Cs
7.5
Ta b l e 4 . 13
Experimental zero-field mobilities
of atomic ions of inert gases in a parent gas
at indicated temperatures. Theoretical values
according to (4.94) are given in parentheses.
The mobilities are given in square centimeters
per volt per second and are reduced to the
normal number density of atoms.
T
,K
300
195
77
He
10.4
˙
1.0 (11)
12
˙
1 (13)
16
˙
1 (17)
Ne
4.1
˙
0.1 (4.0)
4.3
˙
0.3 (4.6)
5.3
˙
0.5 (6.0)
Ar
1.5
˙
0.1 (1.6)
1.9
˙
0.3 (1.8)
2.1
˙
0.1 (2.3)
Kr
0.85
˙
0.1 (0.81)
(0.92)
(1.1)
Xe
0.53
˙
0.01 (0.52)
(0.60)
(0.78)
