Abstract
This papers extends to molecules the moment theory of ion traps and
similar devices where the electric �elds vary with both position and time.
It is based on the Wang Chang-Uhlenbeck-de Boer equation and a series of successive approximations based on the Maxwell model and the assumption that all other moments of the ion distribution function vary much less rapidly with position and time than does the ion number density. Two versions of the theory are presented: a simpler one, based on spherical-polar basis functions, and a more comprehensive one, based on Cartesian functions.
Two-temperature and multi-temperature moment theories were presented for atomic ion motion in traps and similar devices where there are external fields that vary with position and time. The relative advantages and disadvantages of the two theories were briefly discussed. The accuracy of the two-temperature moment theory was demonstrated in a second paper that considered Field-Asymmetric Ion Mobility Spectrometry. The two-temperature theory was then applied to ideal quadrupole ion traps. The purpose of this paper is to extend the theory to molecular ions and/or neutrals.