title: Experimental and modeling study of the ion-molecule association reaction H3O+ + H2O (+M) --> H5O2(+) (+M).
abstract: Experimental results for the rate of the association reaction H3O+ + H2O (+M) --> H5O2(+) (+M) obtained with the Cinetique de Reactions en Ecoulement Supersonique Uniforme flow technique are reported. The reaction was studied in the bath gases M=He and N2, over the temperature range of 23-170 K, and at pressures between 0.16 and 3.1 mbar. At the highest temperatures, the reaction was found to be close to the limiting low-pressure termolecular range, whereas the limiting high-pressure bimolecular range was approached at the lowest temperatures. Whereas the low-pressure rate coefficients can satisfactorily be reproduced by standard unimolecular rate theory, the derived high-pressure rate coefficients in the bath gas He at the lowest temperatures are found to be markedly smaller than given by simple ion-dipole capture theory. This result differs from previous observations on the related reaction NH4(+) + NH3 (+M) --> N2H7(+) (+M). This observation is tentatively attributed to more pronounced contributions of the valence part of the potential-energy surface to the reaction in H5O2(+) than in N2H7(+). Falloff curves of the reaction H3O+ + H2O (+M) --> H5O2(+) (+M) are constructed over wide ranges of conditions and represented in compact analytical form.
authors.affiliation: Physique des Atomes, Lasers, Molécules, et Surfaces, Unité Mixte de Recherche, 6627 du Centre National de la Recherche Scientifique, Université de Rennes 1, 35042 Rennes, France.
authors.forename: S
authors.initials: S
authors.lastname: Hamon
authors.forename: T
authors.initials: T
authors.lastname: Speck
authors.forename: J B A
authors.initials: JB
authors.lastname: Mitchell
authors.forename: B
authors.initials: B
authors.lastname: Rowe
authors.forename: J
authors.initials: J
authors.lastname: Troe