ABSTRACT
Before discussing the physical significance of the fitting procedure described in Chapter 2 and its sensitivity toward the choice of the parameters of the fit, the terms used are briefly reviewed. When an ion of mass m drifts through a bath gas of mass M, there is an electrostatic interaction between them. The interaction potential, V(r), depends on the distance, r, between the interacting species. At the point of closest approach, rm, the depth of the potential curve is ε0 and represents the strongest interaction. The cross section, ΩD, depends on the characteristics of the ion (size, shape, and charge distribution) and neutral molecule (size, shape, and dipole or quadrupole moments). The physical parameters mentioned earlier (V(r), rm, ε0, and ΩD) can be calculated as described in Chapter 2. These calculations are based on the use of other independent parameters, a*, r0, z, and n. These in turn are obtained from the fitting procedure, which involves a comparison of experimentally determined reduced mobility values with that of the calculated values. In the calculations, different choices of these independent parameters are tested until the least deviation between the calculated and measured mobilities is obtained.
