Uniform moment theory for charged particle motion in gases.

Moment equations for the motion of trace amounts of charged particles through dilute gases are developed from the Boltzmann equation. A new method for truncating the coupled moment equations is used to develop differential equations governing the moments in successive approximations. The first approximation equations are shown to agree completely with equations known to describe ion motion in drift-tube mass spectrometers, ion mobility spectrometers, ion traps, and collision-dominated ion cyclotron resonance experiments. Applications to differential mobility spectrometers and other devices are also described.