Internal-Energy Distribution of Molecular Ions in Drift Tubes
The nonreactive motion of trace amounts of a single ion species through a dilute gas in a drift tube is influenced by the gas temperature, T, by the ratio, E/N, of the electric field strength to the gas number density, and by the details of the ion-neutral collisions. On the macroscopic level, this motion is described in terms of the gaseous ion transport coefficients such as the standard mobility, Ko, and the diffusion coefficients, D║ and D┴, parallel and perpendicular to the direction of the electric field. On the microscopic level, this motion is described in terms of the position, velocity and internal-energy state of each ion and neutral as a function of time, since quantum-mechanical effects are completely negligible except for electrons and for very light ions at extremely low values of T and E/N. The connection between these levels of description is through the distribution function fi (r,v,t) for ions in internal state i at position r with velocity v at time t, and through the similar distribution functions for each neutral species.
KeywordsDrift Tube Moment Theory Relative Kinetic Energy Standard Mobility Polyatomic Species
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