Mobilities and longitudinal diffusion coefficients of mass-identified hydrogen ions in H2 and deuterium ions in D2 gas

Abstract

We have measured in a drift tube mass spectrometer the mobilities and longitudinal diffusion coefficients of H⁺, H₃⁺, and H⁻ ions in H₂ gas and D⁺, D₃⁺, and D⁻ ions in D₂ gas. These measurements were made at 300°K and over a substantial range of E/N, where E is the electric field intensity and N is the gas number density. The zero‐field reduced mobilities of the ions in H₂ were determined to be 16.0 ± 0.3, 11.3 ± 0.2, and 43.0 ± 1.3 cm²/V · sec, respectively; the values for the ions in D₂ were 11.7 ± 0.4, 8.07 ± 0.25, and 30.1 ± 0.9 cm²/V · sec, respectively. The fact that the mobilities of H⁻ and D⁻ are so much larger than those of the corresponding positive ions, H⁺ and D⁺, is unexpected and thus far has not been quantitatively explained. Measurements of the longitudinal diffusion coefficients as a function of E/N are in fair agreement with the theoretical predictions of Whealton and Mason. The low‐field diffusion coefficients are in good agreement with the values predicted from the measured mobilities by use of the Einstein equation.