Ab initio determination of the anharmonic vibrational spectra of P2O in the region 200–2000 cm−1

An ab initio quartic force field calculated from a cc-pVTZ basis set at CCSD(T) level of theory is used to compute the vibrational energy levels of diphosphorus oxide, P2O, in the range 200–2000 cm−1. The most important vibrational configurations, constructed from harmonic vibrational wavefunctions, selected by an iterative process by means of a variational perturbational method are diagonalized. The results show a good agreement with the most reliable experimental values such as ν3, the ν1+ν3←ν1 hot band and two postulated Fermi resonances and predict unobserved overtones and combinations bands in the medium IR region.