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.