Ion–molecule reactions in Ar at 296, 195, and 77 °K

Abstract

Ion–molecule reactions have been studied at 296 and 195 °K in Ar gas which has been purified by passage through a Ti furnace. The rate constant k₁ for the reaction, Ar⁺(²P_3/2) + 2Ar → Ar⁺₂ + Ar, was measured in a drift tube at pressures reduced to 0 °C (P₀) of 1.414–3.00 torr. Ions effused from the drift tube and were counted with a TOF mass spectrometer. k₁ was corrected for side reactions with impurities and found to be (2.3±0.2) ×10⁻³¹ and (3.0±0.2) ×10⁻³¹ cm⁶/sec at 296 and 195 °K, respectively. It appears that Ar⁺ in the ²P_1/2 state does not form Ar⁺₂ at these temperatures. An upper limit to the rate constant for the reaction Ar⁺(²P_1/2) + Ar → Ar⁺(²P_3/2) + Ar + energy, was observed to be 2×10⁻¹⁶ cm³/sec at 296 °K. At 77 °K both states of Ar⁺ appear to form Ar₂⁺ with a rate constant of (5.2±0.1) ×10⁻³¹ cm⁶/sec. The rate of formation of Ar⁺₃ and the equilibrium between Ar⁺₃ and Ar⁺₄ were also studied at 77 °K.