Kinetic theory of ion cyclotron resonance collision broadening

Abstract

A rigorous kinetic‐theory treatment of the collision broadening of ion cyclotron resonance lines, valid at all field strengths for arbitrary ion–neutral potentials and mass ratios, is presented. The theory justifies the use, in first approximation, of previously derived equations that are strictly valid only for the Maxwell model of constant mean free time between collisions; now the collision frequency, however, has a detailed molecular interpretation and is not in general constant. Computation of a second approximation shows that convergence is good, and that deviations from Lorentzian line shapes occur at all electric field strengths. The dependence of collision frequency on temperature, gas density, frequency, electric field strength, and ion–neutral potential is compressed into a dependence on a single effective temperature. It is shown how the experimental measurement of such dependence can be used to obtain information on nonreactive ion–neutral interactions.