The
reduced mobility In
this expression, P and _{0}T,
_{0}μ the reduced mass of the buffer gas
and ion, T the effective temperature, and
the momentum transfer collision integral. Thus, by measuring K
we obtain a value for ,
an experimental "cross section"._{0}Kinetic theory indicates that the quantity is a momentum transfer collision integral. It is generally very difficult to calculate theoretically, unless it is calculated for a rigid sphere, in which case is equal to the projection cross section . For a general geometrical shape the projection cross section, which is fairly straight forward to calculate for any shape, is only an approximation for the collision integral.
However,
for similar shapes, differences between
and are similar and
can be corrected for empirically. Differences between
and are largest (up
to 20%) for exotic geometries with large concave surfaces like bowls.
(See e.g. Shvartsburg,
A. A.; Jarrold, M. F. |
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