Mechanism and Rate Constants of Ion–Molecule Reactions Leading to Formation of H+(H2O)n in Moist Oxygen and Air

Abstract

The formation of H+(H2O)n clusters in moist oxygen is of interest since this process must occur in the troposphere and has been observed to occur in the D region of the ionosphere. The reaction mechanism leading from O2+ to H+(H2O)n was investigated with a pulsed electron-beam high-pressure mass spectrometer. At oxygen pressures in the torr range and for [O2]/[H2O]>102 the major reaction proceeds by the sequence O2+→O4+→O2+·H2O→H3O+·OH→H+(H2O)2→H+(H2O)n. The rate constants for all major steps were determined. Rate constants for parallel reactions which may become important at different conditions were also determined.