Competitive reaction and quenching of vibrationally excited O+2 ions with SO2, CH4, and H2O

Abstract

Vibrationally excited O+2 ions injected into a He buffered flow tube react rapidly with SO2 and H2O by charge transfer and with CH4 to produce CH3O+2 , CH+3 , and CH+4 . It is found that the rapidly reacting states at thermal energy are O+2 (v≥2) for SO2 and CH4 and O+2 (v≥3) for H2O, while the lower vibrationally excited states are rapidly quenched. When the reactions of SO2 and CH4 are studied in Ar buffer as a function of kinetic energy it is found that the vibrational temperature of O+2 established through collisional excitation by the Ar buffer is perturbed by quenching collisions with the reactant molecules. This leads to observed reaction rate constants that change with reactant gas concentration. For the reaction of O+2 with CH4 the influence of kinetic and vibrational energy on the branching ratio of the reaction channels has been investigated. The present vibrational relaxation data for O+2 (v) by CH4, in conjunction with other recent measurements, allows a rather detailed picture of the mechanism to be drawn for this complicated reaction that involves the making and breaking of four chemical bonds.