Positive Ion Species and Their Mobilities in Air

Abstract

Positive ion mobilities in dry and laboratory air are measured in the pressure range between 50 and 760 Torr at room temperature by the drift tube method. The apparatus used in this experiment seems to have a 10% systematic error when the results are compared with Bradbury's data. Five ion species are observed in dry air at 760 Torr and their mobilities are measured to be 1.24, 0.96, 0.77, 0.66 and 0.58 cm2/V·sec. In laboratory air at 760 Torr, mobilities of 1.45, 1.28, 0.91 and 0.57 cm2/V·sec are obtained. The molecular form of ions is estimated to be that of O2+(H2O)n in dry air and H+(H2O)n in laboratory air. According to the theory proposed by Moran and Hamill, the water concentration as low as 10-6 Torr is quite enough to form hydrate ions in 70 ms and therefore the mobility of positive ion in air, 1.48 cm2/V·sec, obtained by Bradbury may be responsible for the O2+(H2O)n ion.