Ab initio study for the intermolecular potential of the water-nitric oxidecomplex

Ab initio UMP2 gradient calculations confirm that there are a few stable st ructures of the complex H2O . . . NO ((XII)-I-2). The A' state has three mi nima: the N-bonded anti structure is the global minimum Two other minima ha ve also been located (N-bonded syn and O-bonded anti forms). By contrast, t he A " has one minimum related to a T-shaped form which lies above the A' g lobal minimum (UMP2 gradient optimisation procedure followed by calculation s at the CCSD(T) level). The comparison of the IPES for the A' and A " stat es calculated from a grid of points at the UMP2 level followed by the CCSD( T) calculations for the characteristic points on the IPES demonstrated the failure of the UMP2 calculations for the H2O . . . NO complex. (C) 2000 Els evier Science B.V. All rights reserved.