The water-nitric oxide intermolecular potential-energy surface revisited.

ABSTRACT

The two lowest energy intermolecular potential-energy surfaces (IPESs) of the water-nitric oxide complex are evaluated using the spin-restricted coupled-cluster R-CCSD(T) model and the augmented correlation-consistent polarized-valence triple-zeta basis set extended with a set of the 3s3p2d1f1g midbond functions. A detailed characterization of the IPESs for both the (2)A(') and (2)A(") electronic states in the C(s)-symmetry configurations of the complex is performed. The global minimum for the (2)A(') state represented by the lowest energy of -461.8 cm(-1) is deeper than the global minimum in the (2)A(") state with an energy of -435.2 cm(-1). To explore the physics of the interaction an open-shell implementation of the symmetry-adapted perturbation theory is employed and the results are analyzed as a function of the intermolecular parameters. The electrostatic term shows the strongest geometric anisotropy, while the exchange, induction, and dispersion contributions mostly depend on the intermolecular distance. The energy separation between the (2)A(') and (2)A(") states is largely dominated by electrostatic contribution for long intermolecular distances. In the region of short intermolecular distances the exchange part is as important as the electrostatic one and the induction and dispersion effects are also substantial.