Ion-molecule reaction rates in Ar at 296°K

Abstract

The rate constant k₁ for the reaction Ar⁺(²P_3/2) + 2Ar→Ar₂⁺ + Ar was found to be (2.07±0.20)×10⁻³¹ cm⁶/sec at 296°K. The reaction was studied in a drift tube at pressures reduced to 0°C (P₀) of 1.414–3 torr. Ions effused from the drift tube and were counted with a TOF mass spectrometer. It was found that Ar⁺ in the ²P_1/2 state does not form Ar₂⁺ at room temperature. This fact appears to have been neglected in previous determinations of k₁. Corrections were made for the collision‐induced transition Ar⁺(²P_1/2) → Ar⁺(²P_3/2), where k₂ is the rate constant, and for side reactions with impurities. From experiments at P₀=6 and 9 torr it was found that k_2,Ar≤1.5×10⁻¹⁵ cc/sec. However, recent experiments indicate k_2,Ar−16 cc/sec, so most of the transitions were caused by collisions with an impurity in the Ar.