SYMMETRY-ADAPTED PERTURBATION-THEORY POTENTIAL FOR THE HEK+ MOLECULAR ION AND TRANSPORT-COEFFICIENTS OF POTASSIUM-IONS IN HELIUM

The interaction potential for the HeK+ system has been computed as the sum of attractive and repulsive contributions due to the electrostatic, exchange, induction, and dispersion interactions using the symmetry-adapted perturbation theory and a high-level treatment of electron correlation. The zero of the theoretical potential occurs at 4.704 bohr and the minimum occurs at 5.418 bohr where the potential value is -0.779 mhartree. The potential supports 36 bound rovibrational levels, and the ground state of the HeK+ molecular ion is bound by 125.1 cm(-1). For all interatomic distances the ab initio potential agrees very well with the empirical potential obtained by direct inversion of the K+ mobilities in gaseous helium and disagrees with the potential obtained from the ion-beam scattering cross section data. The ab initio potential has been used to compute the transport coefficients of potassium ions in helium gas over a wide range of temperature and reduced field strength. A very good agreement of the calculated transport coefficients with the preponderance of the existing experimental data is observed. This agreement leads us to believe that the present interaction potential is accurate to within a few percent at all separations between 4.0 and 10.0 bohr and, consequently, represents the most accurate potential available for the HeK+ system.