Flowing afterglow studies of hydronium ion clustering including diffusion effects

The termolecular hydration sequence of H3O+ in helium buffer gas H3O+(H2O)n−1+H2O+He⇄knk−nH3O+(H2O)n+He is studied using the flowing afterglow technique. The rate constants k1, k2, k3, and k−3 and the equilibrium constants K3 and K4 are measured, discussed, and compared with other values. The effects of mass discrimination, ion–electron dissociative recombination, and differing diffusion rates of the ions are considered, and the diffusion coefficients of the ions H3O+(H2O)n, n=0 to 4, are estimated.