Ion-molecule reaction rates in Ar at 296°K

Abstract

The rate constant k1 for the reaction Ar+(2P3/2) + 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 2P1/2 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+(2P1/2) → Ar+(2P3/2), where k2 is the rate constant, and for side reactions with impurities. From experiments at P0=6 and 9 torr it was found that k2,Ar≤1.5×10−15 cc/sec. However, recent experiments indicate k2,Ar<4×10−16 cc/sec, so most of the transitions were caused by collisions with an impurity in the Ar.