Ab initio dynamics of the He + H2+ M HeH+ + H reaction: potential energy surface and quantum mechanical cross-sections

The reaction He + H2+(?,j = 0) M HeH+(?ʹ = 0, jʹ) for ? = 0, 1, 2 and 3 and for scattering energies near the threshold (0.95-1.15 eV) has been studied by calculating ab initio points at MRCI level and ʹexactʹ integral quantum reactive cross-sections. More than 1400 nuclear geometries have been chosen to cover the most important regions for the dynamics, an extended set of points being taken directly on a hyperspherical coordinate grid. A many-body expansion with a large number of terms permits an accurate analytical representation of the potential energy surface with a root-mean-square deviation < 12 meV. The hyperquantization algorithm has been extended to obtain quantum mechanical integral cross-sections which are compared with previous calculations and with experimental results.