Mobility of O+ in He and interaction potential of HeO+

New experimental measurements are reported for the mobility of O+ ions in He gas at 300 K. The accuracy of these new values is estimated as +/- 2.5%, which allows them to serve as a stringent test of a new ab initio potential that we have calculated using the RCCSD(T) method. We employed the aug-cc-pV5Z basis set with counterpoise corrections and took spin-orbit coupling into account. The present experimental values lie below the calculated ones, but the difference becomes statistically significant only at moderate and high values of the ratio of the electric field strength to the gas number density; even there they are only marginally significant