Measurement of the rate coefficient of the reactions H+ + 2H2 → H3+ + H2 and D+ + 2D2 → D3+ + D2 in a drift tube mass spectrometer

Abstract

The rate coefficient of the reaction H⁺ + 2H₂ → H₃⁺ + H₂ has been measured at a gas temperature of 300 °K and over a pressure range 0.25–0.50 torr. The transport properties and average energy of a given species of ion drifting in a gas in a uniform electric field are determined by E/N, where E is the electric field intensity and N is the gas number density. E/N is expressed in units of the townsend (Td), where 1 Td = 10⁻¹⁷ V · cm². Our measurements were made over a range 25–50 Td, where the lower value corresponds to an average energy for the reacting H⁺ ions which is very close to the thermal energy of the H₂ molecules at 300 °K. No systematic variation of the rate coefficient was observed over the range of E/N which was covered. The measurements were made with a drift tube mass spectrometer and involved the detailed analysis of the arrival time spectra of the product ${\mathrm{H}}_3^{+}$ ion. The rate coefficient was evaluated to be (3.05 ± 0.15) × 10⁻²⁹ cm⁶/sec. The same result was also obtained for the reaction D⁺ + 2D₂ → D₃⁺ + D₂.