ИСТИНА

We report on the main results obtained using a state-of-the-art implementation of the operator version of the second-order canonical Van Vleck vibrational perturbation theory (CVPT2) for analyzing the vibrational spectra of 2,3,3,3-tetrafluoropropene (H2C=CF–CF3, also designated as HFO-1234yf or R-1234yf), a promising substitute of 1,1,1,2-tetrafluoroethane as a refrigerant. In addition to a thorough assignment of all the vibrational features in the range 9500-30 cm−1, the integrated intensities in the range 6300-400 cm−1 were accurately determined. The remarkable agreement between the experimental intensities, observed for the most relevant absorptions, and the corresponding ab initio values confirmed the reliability of the computed dipole moment surface. An ab initio full quartic potential energy surface was employed to compute anharmonic energy levels using numerical-analytic implementation of CVPT2; the effects related to the size of the basis set (up to four-quanta) chosen for the subsequent VCI stage were studied. The analysis of the Fermi and Darling-Dennison resonances revealed that several fundamental states form complex polyads with neighboring multi-quanta states, which cannot be properly described with a pairwise interaction model. We also investigated the mechanism of reproducing resonance doublets in higher regions with additional excitation of modes and its potential application for a better understanding of IR/Raman spectra in the NIR region.