The interaction of OH(X2Π) with H2: Ab initio potential energy surfaces and bound states

Abstract

For the interaction of OH(X 2 ) with H 2 , under the assumption of fixed OH and H 2 bond distances, we have determined two new sets of four-dimensional ab initio potential energy surfaces (PES's). The first set of PES's was computed with the multi-reference configuration interaction method [MRCISD+Q(Davidson)], and the second set with an explicitly correlated coupled cluster method [RCCSD(T)-F12a] sampling the subset of geometries possessing a plane of symmetry. Both sets of PES's are fit to an analytical form suitable for bound state and scattering calculations. The CCSD(T) dissociation energies (D 0 ) of the OH-para-H 2 and the OH-ortho-H 2 complexes are computed to be 36.1 and 53.7 cm −1 . The latter value is in excellent agreement with the experimental value of 54 cm −1 .

Rotationally inelastic scattering of OH by molecular hydrogen: Theory and experiment

“…In particular, the positions of both the sharp and broad resonances are shifted slightly. In previous work, 24 we showed that the CCSD(T) and MRCI PES's were quite similar. In particular, the computed dissociation energies D 0 of the OH-ortho-H 2 and OH-para-H 2 complexes differed by only 2 cm .…”

“…The PES's employed in the determination of the cross sections are taken from Ref. 24. As noted in the Introduction, we computed PES's from fits to ab initio points obtained with both MRCISD+Q(Davidson) and RCCSD(T)-F12a calculations [denoted below as MRCI and CCSD(T), respectively].…”

“…In our work on the calculation of the OH-H 2 PES's, 24 we carried out additional calculations on the interaction energy at several nuclear geometries, beyond full MRCI and RCCSD(T) calculations of the PES's. The explicitly correlated CCSD(T)-F12a calculations and canonical CCSD(T) calculations with complete basis set (CBS) extrapolation gave similar results.…”

“…In particular, for both sets of PES's, bound-state calculations of the dissociation energies (D 0 ) of the OH-ortho-H 2 and OH-para-D 2 complexes agreed well with experimental measurements. 25 In this paper, we report new experimental measurements as well as calculations, based on our new PES's, 24 of state-tostate cross sections for OH-H 2 rotationally inelastic collisions. The range of collision energies investigated was lower than in the previous study of OH-D 2 collisions, 10 which also employed a Stark decelerator 11 to vary the collision energy.…”

“…In a recent work, 24 we used two methods for the calculation of the OH-H 2 PES's: multi-reference configuration interaction method [MRCISD+Q(Davidson)] and explicitly correlated spin-restricted coupled-cluster method with single-, double-, and (perturbative) triple excitations [RCCSD(T)-F12a]. The former method is applicable for any nuclear geometry while the latter requires a plane of symmetry but allows a more complete treatment of electron correlation.…”