Properties of H-2(+) relevant to the He-H-2(+) intermolecular potential: asymptotically increasing multipole moments, polarizabilities and dispersioncoefficients

The quadrupole moment and polarizabilities of H-2(+) and the C-6 dispersion coefficients for He-H-2(+) are fitted to functional forms with the correct limiting behaviour for both large and small values of the H-H bond length r. Both the quadrupole moment and the dispersion coefficients increase quad ratically with r at long range, while the polarizabilities increase exponen tially. The reasons for the behaviour are analysed.