title: Ion kinetics in Ar/H2cold plasmas: the relevance of ArH.
abstract: The recent discovery of ArH+in the interstellar medium has awakened the interest in the chemistry of this ion. In this work, the ion-molecule kinetics of cold plasmas of Ar/H2is investigated in glow discharges spanning the whole range of [H2]/([H2]+[Ar]) proportions for two pressures, 1.5 and 8 Pa. Ion concentrations are determined by mass spectrometry, and electron temperatures and densities, with Langmuir probes. A kinetic model is used for the interpretation of the results. The selection of experimental conditions evinces relevant changes with plasma pressure in the ion distributions dependence with the H2fraction, particularly for the major ions: Ar+, ArH+and H3+. At 1.5 Pa, ArH+prevails for a wide interval of H2fractions: 0.3<[H2]/([H2]+[Ar])<0.7. Nevertheless, a pronounced displacement of the ArH+maximum towards the lowest H2fractions is observed at 8 Pa, in detriment of Ar+, which becomes restricted to very small [H2]/([H2]+[Ar]) ratios, whereas H3+becomes dominant for all [H2]/([H2]+[Ar]) > 0.1. The analysis of the data with the kinetic model allows the identification of the sources and sinks of the major ions over the whole range of experimental conditions sampled. Two key factors turn out to be responsible for the different ion distributions observed: the electron temperature, which determines the rate of Ar+formation and thus of ArH+, and the equilibrium ArH++ H2⇄ H3++ Ar, which can be strongly dependent of the degree of vibrational excitation of H3+. The results are discussed and compared with previously published data on other Ar/H2plasmas.
authors.affiliation: Instituto de Estructura de la Materia, IEM-CSIC, Serrano 123, 28006 Madrid, Spain.
authors.forename: Miguel
authors.initials: M
authors.lastname: Jiménez-Redondo
authors.affiliation: Instituto de Estructura de la Materia, IEM-CSIC, Serrano 123, 28006 Madrid, Spain.
authors.forename: Maite
authors.initials: M
authors.lastname: Cueto
authors.affiliation: Instituto de Estructura de la Materia, IEM-CSIC, Serrano 123, 28006 Madrid, Spain.
authors.forename: José Luis
authors.initials: JL
authors.lastname: Doménech
authors.affiliation: Instituto de Estructura de la Materia, IEM-CSIC, Serrano 123, 28006 Madrid, Spain.
authors.forename: Isabel
authors.initials: I
authors.lastname: Tanarro
authors.affiliation: Instituto de Estructura de la Materia, IEM-CSIC, Serrano 123, 28006 Madrid, Spain.
authors.forename: Víctor J
authors.initials: VJ
authors.lastname: Herrero