An ab initio study of the Ar-NO(A 2Σ+) intermolecular potential

More complete molecular dynamics simulations of NO doped Ar solid upon photoexcitation of the impurity should include effects of angular variations of Ar-NO intermolecular potential. This is the main reason for presenting in this work an ab initio study of the Ar-NO(A (2)Sigma(+)) intermolecular potential. Ab initio calculations were carried out at the level of CASSCF-MRCI, with the aug-cc-pVTZ basis sets. In order to evaluate the influence of the quadruple excitations on the topology of the potential energy surface (PES), two cases were considered, that is, with and without taking into account Davidson's correction for quadruple excitations during the calculations. An analytical representation of the PES has been obtained as a function of the Jacobi coordinates of the system. In general, the PES is repulsive, except for linear directions, where two shallow wells appear. When quadruple excitations are considered, wells are located at 4.2 A degrees (alpha=0 degrees) and 6.08 A degrees (alpha=180 degrees) with energies of -20 and -15 cm(-1), respectively; and when are not considered, wells are located at 6.1 A degrees (alpha=0 degrees) and 6.8 A degrees (alpha=180 degrees) with energies of -15 and -10 cm(-1), respectively. For distances beyond 7 A degrees, it is observed a very low energy decay and a rapid tendency to isotropic interactions.