Ion–ion recombination studies in ambient helium and argon at atmospheric densities

We have measured the dependence on gas density of the recombination rate for the reaction H3O+(H2O)n+NO−3→neutrals for n=2,3 in helium at densities from 0.3 to 1.2 NL and in argon from 0.2 to 0.9 NL (NL =Loschmidt’s number). We find that three-body recombination accounts for only part of the total observed recombination rate. The enhancement of mutual neutralization by the ambient gas appears to dominate the recombination process at low densities. A simple model is given which reproduces the experimental data fairly well.