SPECTROSCOPIC CONSTANTS AND POTENTIAL-ENERGY FUNCTIONS OF OCCL-CLUSTER METHOD(, ONP, ONS+, ARCN+, OCS, AND NCCL USING THE COUPLED)

Large basis set ab initio calculations have been carried out on the th ree-dimensional near-equilibrium potential energy surfaces of the spec troscopically unknown species OCCl+, ONP, ONS+, and ArCN+ and the isoe lectronic reference molecules OCS and NCCl, using a correlation consis tent polarized valence quadruple zeta (cc-pVQZ) basis set and the coup led cluster method with single and double substitutions, augmented by a perturbative estimate of triple excitations [CCSD(T)]. A complete se t of spectroscopic constants for each species has been obtained from t he CCSD(T)/cc-pVQZ potential energy surfaces using the standard second -order perturbation theory formulas. In order to predict equilibrium b ond distances of the unknown species as accurately as possible, their resulting CCSD(T) structures have been corrected based on identical ca lculations on both the diatomics CO, CN, NO, CS, CCl+, and NP and the linear triatomics OCS and NCCl. The second-order spectroscopic constan ts and anharmonic force fields for OCS and OCCl+ previously calculated with the MP4SDQ and CISD(s) methods are in good agreement with the pr esent CCSD(T) results. (C) 1997 American Institute of Physics.