Environmental Engineering Reference
In-Depth Information
Figure 4.21
The recombination coefficient of positive and negative ions as a function of the gas
density. 1 - region of pairwise ion-ion recombination; 2 - region of three body recombination of
positive and negative ions in a gas; 3 - region of high pressures.
Region 3 in Figure 4.21 is described by th
e La
ngevin theory, and (4.129) gives the
order-of-magnitude estimate
e
/(
N
p
μ
) for the recombination coefficient
in this region if we assume that the polarization interaction potential determining
the ion-atom scattering process acts. The transition between regions 2 and 3 is
associated with the number density
α
3
T
3/2
/(
e
3
p
N
2
),
and this number density corresponds to the largest recombination coefficient,
α
μ
1/2
T
3/2
. The relevant physical process is pairwise ion-ion recombi-
nation if the cross section corresponds to elastic scattering of particles experiencing
the Coulomb interaction. Thus, the maximum recombination coefficient has the
same order of magnitude as the elastic rate constant of ions.
e
4
max
Figure 4.22
The recombination coefficient of positive and negative ions in air as a function of
pressure. The curve is an approximation of experimental data given by open circles [106] and
closed circles [107].
