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+(2P3/2) + 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 2P1/2 state does not form Ar+2 at these temperatures. An upper limit to the rate constant for the reaction Ar+(2P1/2) + Ar → Ar+(2P3/2) + 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.