Ion-Molecule Reactions of NH3+ by Photoionization

Abstract

Photoionization-efficiency curves were measured for NH3+, and NH4+, and H3O+ ions in NH3 gas and in gaseous mixtures of NH3 and H2O. The results are interpreted to determine how the relative reaction cross section depends on the vibrational energy of the NH3+ ion for the reactions NH3+ + NH3→NH3+ + NH2, NH3+ + H2O→NH4 + OH. The cross section for Reaction (1) decreases with increasing vibrational energy while that for Reaction (2) is nearly independent of vibrational energy. The results are discussed in terms of the formation of an intermediate complex and in terms of stripping models. The upper limit of the proton affinity was determined to be ≥ 8.54 eV for NH3 and ≥ 7.0 eV for H2O.