Spectroscopic constants and potential energy functions of OCCl+, ONP, ONS+, ArCN+, OCS, and NCCl using the coupled cluster method

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