Infrared vibrational spectra and absolute intensities of fundamental bands of bis(trifluoromethyl)ketene: Ab initio interpretation using the second order operator Van Vleck perturbation theory

Abstract

Bis(trifluoromethyl)ketene (BTFMK, (CF3)2CCO) is an important chemical compound for the organic synthesis and in polymer chemistry. In this work, IR spectra of gaseous BTFMK were recorded in the range of 2280–400 cm−1 with a resolution of 1 cm−1. The experimental absolute IR intensities of 17 fundamental bands of BTFMK were measured and juxtaposed with ab initio anharmonic ones. The molecular structures, semi-diagonal quartic potential energy surfaces (PES), and cubic surfaces of dipole moment components (μ^α) were calculated at the MP2/cc-pVTZ level of theory. The predicted frequencies were refined by substituting the harmonic part of PES with the MP2/cc-pVQZ counterparts. The second-order operator canonical Van Vleck perturbation theory (CVPT2) was employed for predicting anharmonic energy levels, IR integral intensities and full experimental (re)-assignments. The deviation of predicted IR intensities from observations for ν1−ν4, ν6, ν7, ν9, ν14, ν15, ν22 was ≤12% on average. Three predicted Fermi resonances were experimentally identified: ν14/ν6+ν20, ν17/ν9+ν21 and ν18/ν7+ν25.