Vibronic spectra, ab initio calculations, and structures of conformationally non-rigid molecules of oxalyl halides in the ground and lowest excited electronic states. Part III: Theoretical investigation of oxalyl fluoride

Abstract

a b s t r a c tWe present a theoretical investigation of oxalyl fluoride (COF) 2 in the ground and the four lowest excited (two singlet and two triplet) electronic states of the n,p*-type mainly with the CASPT2(8-6)/cc-pVTZ method. Geometries, vibrational frequencies, potential energy functions of internal rotation, and adiabatic electronic transition energies were obtained. The conformer energy difference and the barrier to internal rotation in the ground electronic state were extrapolated to the complete basis set limit. The planar trans and cis conformations were the most stable configurations for all five electronic states under study. We found that the allowed electronic transition of the cis conformer has a transition energy that is significantly higher than that predicted in previous studies. For the excited states, the internal rotation was found to be accompanied by significant non-planar distortion of both carbonyl fragments, indicating strong coupling between these molecular motions.

Vibronic spectra, ab initio calculations, and structures of conformationally non-rigid molecules of oxalyl halides in the ground and lowest excited electronic states. Part V: Oxalyl chloridefluoride (COCl–COF)

“…We found the wave functions of the oxalyl chloridefluoride in the excited electronic states to be strongly multiconfigurational especially for the structures skewed relative to C-C bond similar to the (COF) 2 and (COCl) 2 molecules [2,3]. In some cases, even in minima the wave function can be represented by two or three configurations with comparable weights.…”

“…Two systems of vibronic bands, 3480 Å and 3870 Å , were found. These systems were assigned to the singlet-singlet A 1 A 00 X 1 A 0 and the singlet-tripletã 3 A 00 X 1 A 0 electronic transitions of the trans conformer, respectively. The transitions of the second conformer were not found in spectrum [5,6].…”

“…As in glyoxal (see, e.g., [13]), oxalyl fluoride [3] and oxalyl chloride [2], the four lowest excited states of oxalyl chloridefluoride are two singlet and two triplet states, which arise from n ? p* excitations.…”

“…For oxalyl chloridefluoride, there are no experimental data on geometries of conformers in the ground electronic state. The comparison of calculated values could be made only with geometric parameters of oxalyl fluoride (COF) 2 and oxalyl chloride (COCl) 2 obtained experimentally [29,30] or theoretically [2,3]. In general, if the CCSD(T)/ cc-pVTZ or cc-pVQZ values are compared, the respective geometric parameters of CFO, CClO fragments of COCl-COF, (COF) 2 , and (COCl) 2 molecules are very similar.…”

“…1 The first four parts are devoted to the experimental and theoretical investigations of oxalyl chloride (COCl-COCl) [1,2] and oxalyl fluoride (COF-COF) [3,4].…”