Quantum Mechanical Investigation of the HeH3+ Energy Surface

Abstract

Results of an ab initio calculation of the potential surface of HeH₃⁺ are reported, with emphasis on establishing the low energy reaction paths for ${\mathrm{HeH}}^{+}+{\mathrm{H}}_2=\mathrm{He}+{\mathrm{H}}_3^{+}$ within the single configuration molecular orbital (SCF) approximation. Using a basis set of (9s1p/4s1p) Gaussian functions centered on the (He/H) nuclei, the lowest potential energy paths are found to follow C_2v symmetry, and these are examined in greater detail. A small number of configuration interaction (CI) calculations are reported involving all single and double excitations from the single configuration. From these calculations about 80% of the total correlation energy (or 90% of the p limit correlation energy) is obtained for the separated two electron fragments, and the CI surface is indicated to lie parallel to the SCF surface to within a few percent of the total energy change of the reaction. The C_2v minimal energy reaction path is found to decrease monotonically with no reaction barriers or local minima, with the heat of reaction (at 0°K) calculated to be 2.63 eV exothermic from the SCF results and 2.62 eV exothermic from the CI results.