The equilibrium structure and spectroscopic constants of HCP - an ab initio study

The molecular parameters of phosphaethyne, HCP, have been determinned in large-scale ab initio calculations using the coupled cluster method, CCSD(T), and basis sets of double- to quintuple-zeta quality. The effect of core correlation on the structural parameters was investigated. The equilibrium structure of the molecule was found to be linear, with the bond lengths r(HC) = 1.0706 Å and r(CP) = 1.5399 Å. The full anharmonic quartic force field was determined. The spectroscopic constants of HCP were calculated using perturbation theory and accounting for the effects of a Fermi resonance. The calculated molecular constants were found to be in excellent agreement with experimental data.