Interaction potential and gaseous ion mobility of CO+ions in He

An effective spherical interaction potential for HeCO+ and values for the momentum-transfer collision integral are obtained from experimental ion mobility data by using the direct inversion method. The potential is fitted to a Morse–Spline–van der Waals (MSV) model potential. Consistency is checked by calculating collision integrals and the mobilities of CO+ ions in He gas from the MSV potential and showing that they agree with the experimental data. The separation- and angle-dependent interaction potential energy surface is calculated from the spin-unrestricted, fourth-order Moller–Ploesset theory with single, double, triple and quadruple excitations, using a 6-311++G(3df,3pd) basis set while correcting for basis set superposition error. Full and partial versions of the ab initio potentials are used to determine the transport cross-sections for the collisions of CO+ with He as a function of the collision energy at fixed angles between the C–O bond axis and the internuclear axis. Finally, the transport coefficients of CO+ ions moving through He are calculated accurately, over a wide range of reduced electric field and gas temperature, using an extension of the Monchick–Mason approximation.