Potential functions of internal rotation of the methacryloyl fluoride molecule in the ground (S0) and excited (S1) electronic states

The potential functions of internal rotation V(phi) (PFIR) of methacryloyl fluoride (MAF) in the ground (S-0) and excited (S-1) electronic states were reconstructed using the TORSIO program from experimental energy levels of the torsional transitions in the s-trans- and s-cis isomers. The energy levels were obtained from the analysis of the vibrational structure in the high-resolution gas-phase UV spectrum. The (S-0) and (S-1) equilibrium geometries of the s-trans- and s-cis rotational isomers of MAF as well as structural parameters for a set of points along the relaxed geometry scans, which were used to find expansion coefficients of kinematic function F(phi) in the Fourier series, were calculated using extended multiconfiguration quasi-degenerate perturbation theory, XMCQDPT2/SA(2)-CASSCF(6,5)/aug-cc-pVTZ. The ground (S-0) state calculations were also done at the MP2 level of theory. In (S-0) state, parameters V-n, barriers of internal rotation Delta H-double dagger and Delta H of MAF isomers were calculated using two theories. The calculated values of V-n, Delta H-double dagger, Delta H in (S-0) state are in good agreement with those derived from the vibrationally resolved UV spectrum of MAF in the gas phase. Within the one-dimensional model, the experimentally derived barrier heights that hinder internal rotation in MAF were found to be 2100 +/- 50 cm(-1) and 4950 +/- 250 cm(-1) in the (S-0) and (S-1) states, respectively. The parameters V-n and Delta H-double dagger in (S-1) state are determined for first time. (C) 2018 Elsevier B.V. All rights reserved.