Ground and first-excited global potential energy surfaces of the H2O+-He complex: Predictions of ion mobilities

Ion mobilities of H2O+ drifting in helium are calculated and compared with experiment. These calculations employ global potential energy surfaces of the H2O+-He complex, which in the present case were calculated ab initio at the unrestricted MP2 level of theory using a basis set of aug-cc-pVTZ quality, and treating the ion as a rigid body. Details are presented of the general characteristics of both the ground and first-excited electronic states of the complex. Although only the ground-state surface was used for the mobility calculations, the ab initio determination of the ground state necessitated the inclusion of the first-excited state owing to the presence of a crossing between the two. This crossing is also described. Mobilities calculated from the global surfaces are in good agreement with experiment. (C) 2004 Wiley Periodicals, Inc.