Research on the Potential Energy Surface and Anharmonic Spectra of the PH3

The potential energy surface and vibration spectrum of the interstellar molecule Phosphine (PH₃) are calculated ab initio by using the MOLPRO 2018 quantization program package based on the high-precision coupled CCSD(T)-F12a theoretical method and the cc-pVTZ-F12 basis set. Firstly, the equilibrium geometric structure of the PH₃ molecule is calculated by using the coupled clusters CCSD, CCSD(T), CCSD(T)-F12a, and the Møller–Plesset perturbation theory to second order (MP2) methods in combination with different basis sets, and it is found that the optimized structure obtained at the CCSD(T)-F12a/cc-pVTZ-F12 level is in agreement with the experimental values. In addition, there are potential wells that appear in the two-dimensional relative potential energy surface of the vibrational mode containing q₂, which is very different from the previously studied potential energy surface of the Phosphaethyne (HCP) molecule. Secondly, the vibrational multi-configuration self-consistent field (VMCSCF) and the vibrational multi-reference configuration interaction (VMRCI) are used to calculate the PH₃ fundamental frequencies, overtones, and combination frequencies, and found that the degenerate phenomenon between the fundamental frequencies and the Fermi resonance between overtones and combination frequencies. Finally, the infrared and Raman spectra are plotted using the calculated anharmonic frequencies, and the above phenomena can also be observed from the spectrogram. This paper provides a valuable reference for the study of interstellar molecules containing P.