Quantum Monte Carlo study on the 11A' and 21A' potential energy surfaces of He + H2 system

Quantum Monte Carlo (QMC) calculations of selected points on the potential energy surfaces (PESs) of the ground state (11A') and the first excited singlet state (21A') of the He + H2 system are carried out to test the accuracy of existing PES data for use in energy-transfer collision studies. A fixed-sample optimization of the correlation function parameters is performed at each geometry. The calculations confirm an intersection region over a range of geometries and therefore provides an explanation for the high quenching rate of H2(B 1Σu+) by He found experimentally. This system provides yet another example of the intersection of two surfaces of the same symmetry for a polyatomic system. In general, the QMC total energies are significantly lower than those determined in previous theoretical work