Vibration energy levels of the PH_3, PH_2D, and PHD_2molecules calculatedfrom high order potential energy surface

摘要

Vibrational energy levels of the PH_3, PH_2D, and PHD_2molecules were calculated from the newextended potential energy surface (PES) determined in this work. The coupled-cluster approach withthe perturbative inclusion of the connected triple excitations CCSD(T) and correlation consistentpolarized valence basis set cc-pV5Z was employed in the ab initio calculations of electronic groundstate energies. The contribution of relativistic effects to the overall electronic energy surface wascomputed using quasirelativistic mass-velocity-Darwin approach. These ab initio points were fittedby a parametrized function with one parameter empirically adjusted. The grid of 11 697 geometricalnuclear configurations covers a large domain of the six dimensional internal coordinate space andwas designed to provide vibration energy levels of phosphine molecule up to 7000 cm ~(-1)above thezero point vibration energy with reasonable accuracy. The analytical representation of the PES wasdetermined through the expansion in symmetry adapted products of nonlinear internal coordinatesfor various orders of analytical expansions up to the tenth order. The dependence of calculatedvibration energy levels on the analytical representation of PES and on the coordinate choice wasstudied. Calculated vibration levels are in very good agreement with observations: The root meansquares deviation between theoretically calculated and observed band centers is 1.4 cm ~(-1)for PH_3,0.4 cm ~(-1)for PH_2D, and 0.6 cm~(-PHD_2.