Effects of a small amount of H2O on negative ion mobility and ion-molecule reactions in O2 at atmospheric pressure

Abstract

In this study, we have measured the negative ion mobility in O₂ at high pressures with a little amount of H₂O concentration between 15 and 17,000 ppb. After that, we carried out a Monte Carlo simulation using mobility of electrons, that of the ions obtained in the measurements, and rate coefficients of ion-molecule reactions. As a result, the mobility value 2.39 cm²/V·s of O₄¯ is obtained in ultrahigh purity O₂ of which the H₂O concentration is between 15 and 100 ppb. Moreover, the mobility decreases with the H₂O concentrations at which the ion species are considered to be O₂¯·(H₂O)_n (_n = 1, 2, 3). Then, we compared the experimental result with that of the simulation and estimated the ion mobility and rate coefficients of ion molecule reactions. Simulation results using estimated values of the ion mobility and rate coefficients agree well with measurement results.