Drift and clustering of daughter negative ions of H sub(2)O in parent gas

• Published in: Journal of physics. D, Applied physics Vol. 46; no. 3; pp. 035201 - 1-7
• Main Authors: de Urquijo, J, Bekstein, A, Ruiz-Vargas, G, Gordillo-Vazquez, F J
• Format: Journal Article
• Language: English
• Published: 23.01.2013
• Subjects: Clusters; Drift; Field strength; Gas pressure; Negative ions; Parents; Rate constants; Simulation
• ISSN: 0022-3727
• DOI: 10.1088/0022-3727/46/3/035201

The mobility of daughter negative ions of H sub(2)O in parent gas has been measured with a pulsed Townsend technique over the density-reduced field strength, E/N, range 9-100 Td and a pressure range 2-16 Torr. It has been found that the mobility of the anions is dependent on the gas pressure. Using a transport theory considering the influence of the permanent dipole field of H sub(2)O, we have found that the pressure-dependent mobilities can be associated with a series of cluster ions of the type OH super(-) (H sub(2)O) sub(n) (n = 1-3), with the mass of the cluster species increasing with the total gas pressure. Also, the mobility of H super(-) and OH super(-) could be estimated. Using a Townsend avalanche simulator we have been able to explain the measured ionic currents in terms of an ion-molecule reaction scheme with a single set of swarm and reaction coefficients for each value of the density-reduced field strength, E/N, at several pressures. Regarding the positive ions, the only drifting ion is H sub(3)O super(+), the mobility of which could be estimated. The rate constants relative to the formation of the OH super(-)(H sub(2)O) sub(n) (n = 1-3) species were also derived from this study.