Properties of H2+ relevant to the He-H2+ intermolecular potential:: asymptotically increasing multipole moments, polarizabilities and dispersion coefficients

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 quadratically with r at long range, while the polarizabilities increase exponentially. The reasons for the behaviour are analysed.