Mobilities of various mass-identified positive ions in helium and argon

Abstract

Measurements at room temperature with a flow-drift tube have been made of the mobilities of the following mass-identified positive ions: H3+, O+, CO+, COH+, Ar+, ArH+, O2+, O2H+, O2H2+, NH3+, NH4+, CH5+, CO2+, NO+, and N2OH+ in helium and COH+, CO2+, and N2OH+ in argon. The measurements were obtained over the range 2 ? E/N ? 135 Td for helium and 5 ⩽ E/N ? 200 Td for argon (1 Td = 10−17 V⋅cm2). The similarities of the E/N dependence of the mobilities are discussed. The reduced zero-field mobilities obtained here and in other studies of ions in helium and argon are compared to the predicted mobilities of the point-charge, induced-dipole, or ’’Langevin,’’ model. The discrepancies are smaller for the more polarizable argon.