Ion mobility measurements for O₂⁺in helium gas at 4.35 K

The mobility of O 2 + in He has been measured using a liquid helium cooled, selected ion drift tube at 4.35 K. The dependence of mobility on effective temperature, for O 2 + , is similar to that measured previously for rare gas ions moving in He. The mobility reaches a maximum at between 500 K and 600 K where it is in reasonable agreement with the existing room temperature measurements. Below 70 K there is a region in which mobility is constant, but lower than the polarization limit, and below 10 K, mobility decreases sharply. Although clustering reactions occur at low effective temperature, it is not certain that they are responsible for these phenomena, and although a quantum mechanical orbiting resonance is expected to occur at low collision energies, there are no theoretical predictions of its importance for the O 2 + -He system.