The interaction of NO(X²Π) with H₂: Ab initio potential energy surfaces and bound states

We determine from first principles two sets of four-dimensional diabatic potential energy surfaces (PES's) for the interaction of NO(X²Π) with H₂, under the assumption of fixed NO and H₂ bond distances. The first set of PES's was computed with the explicitly correlated multi-reference configuration interaction method [MRCISD-F12 + Q(Davidson)], and the second set with an explicitly correlated, coupled-cluster method [RCCSD(T)-F12a] with the geometry scan limited to geometries possessing a plane of symmetry. The calculated PES's are then fit to an analytical form suitable for bound state and scattering calculations. The RCCSD(T)-F12a dissociation energies (D₀) of the NO-para-H₂(ortho-D₂) and the NO-ortho-H₂(para-D₂) complexes are computed to be 22.7 (31.7) and 23.9 (29.2) cm^-1, respectively. The values calculated with the MRCISD-F12 + Q PES's are 21.6 (31.1) and 23.3 (28.4) cm^-1, respectively.