Negative ion mobility in O₂ and O₂⁄O₃ mixtures [1] is measured using a high-pressure ion drift tube, which was developed by Gosho [2] and has been improved in our laboratory. Since the Geiger counter, i.e., positive corona gap is used as an ion detector, the experiments are capable of being conducted under the atmospheric condition. The drift length of ion is variable from the outside of the chamber. The reduced mobility of 2.3 cm2/V·s is obtained as constant value with respect to the reduced electric field intensity. The value is consistent with the zero field mobility of O₂^- in O₂ reported by Snuggs [3] et al. and McKnight [4]. The experiment is now being expanded to the investigations in O₂/O₃ mixture. The result of our preliminary experiments suggests that the mobility in the mixtures is decreased by increasing the O₃ concentration. Our final goal is to interpret these facts with referring the electron attachment process [5].

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