The potential energy surface and vibrational-rotational energy levels of HCP

The potential energy surface of phosphaethyne, HCP, has been determined from large-scale ab initio calculations using the coupled-cluster method, CCSD(T), with basis sets of triple- to quintuple-zeta quality. The vibrational-rotational energy levels of the HCP molecule have then been calculated using the variational method and have been further characterized by the spectroscopic constants determined using the perturbational approach. The effects of the one-particle basis set and of core correlation on the calculated molecular parameters have been investigated. The spectroscopic constants determined at the most advanced level of theory used here are found to be in excellent agreement with experimental data. (C) 1997 Elsevier Science B.V.