Electronic excitations of fluoroethylenes

Abstract

Several lowest-lying singlet electronic states of vinyl fluoride, trans-, cis-, and 1,1-difluoroethylene, trifluoroethylene, and tetrafluoroethylene were investigated by using symmetry-adapted cluster configuration interaction theory. Basis sets up to Dunning's aug-cc-pVTZ augmented with appropriate Rydberg functions were utilized for the calculations. Calculated excitation energies show a good agreement with the available experimental values. Even in the troublesome pi-->pi(*) transitions, the excitation energies obtained in the present study agree well with the experimental values except in one or two fluoroethylenes. Strong mixing between different states was noticed in a few fluoroethylenes; especially the mixing is very strong between pi-pi(*) and pi-3ppi states in trifluoroethylene. No pure pi-sigma(*) excited state was found in almost all the fluoroethylenes. Several assignments and reassignments of features in the experimental spectra were suggested. The present study does not support the existing argument that the interaction between the pi-pi(*) and sigma-sigma(*) states is the reason behind the blueshift of around 1.25 eV in the pi-pi(*) excitation energy of tetrafluoroethylene. Possible reasons, including structural changes, for this shift are discussed in detail. Several low-lying triplet excited states were also studied.

A CASSCF and CASPT2 study of the photochemistry of 1,1- and 1,2-difluoroethylenes

“…As it can be seen, the MS-CASPT2 energies are in good agreement with the experimental data [37,39] and with the SAC-CI calculated values [40]. In the 1,1-DFE the pp * [31].…”

“…0.2 eV. This state is overestimated by 0.3 eV by the SAC-CI calculations in all difluoroethylenes [40].…”

“…The Z state is not described in the SAC-CI calculations of Arulmozhiraja et al [40]. Nevertheless, as it will be shown in the following sections, this state plays a role in the photophysics of difluoroethylenes because it is involved in the relaxation mechanisms.…”

“…Recently, a high resolution VUV photoabsorption spectrum of 1,1-difluoroethylene has been reported by Limão-Vieira in the range from 6.2 to 10.8 eV, with a careful assignment of the Rydberg and vibrational transitions [39]. Calculations of the excitation energies of mono-and di-fluoroethylenes are presented, up to our knowledge, only in a recent paper of Arulmozhiraja et al [40] and in another one from the Lisckha's group, devoted to the vinyl fluoride [8]. In this latter paper, stationary points and CIs are also presented and the photodynamics of vinyl fluoride is discussed in the light of these structures.…”

“…For the sake of comparison, Table 1 also includes available experimental values [37,39] and the symmetry-adapted cluster configuration interaction (SAC-CI) calculated values of Arulmozhiraja et al [40].…”