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.