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

Bis(trifluoromethyl)ketene (BTFMK, (CF3)(2)C = C = O) 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 ((mu) over cap (alpha)) 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 v(1) - v(4) , v(6) , v(7) , v(9) , v(14) , v(15) , v(22) was <= 12% on average. Three predicted Fermi resonances were experimentally identified: v(14)/v(6) + v(20) , v(17)/v(9) + v(21) and v(18)/v(7) + v(25) . (c) 2021 Elsevier Ltd. All rights reserved.