Electronic excitations of fluoroethylenes

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.This study has been supported by the Grant for Creative Scientific Research from the Ministry of Education, Science, Sports, and Culture of Japan

Electronic spectra and photodissociation of vinyl chloride: A symmetry-adapted cluster configuration interaction study

The vertical absorptionspectrum and photodissociation mechanism of vinyl chloride (VC) were studied by using symmetry-adapted cluster configuration interaction theory. The important vertical π→π* excitation was intensively examined with various basis sets up to aug-cc-pVTZ augmented with appropriate Rydberg functions. The excitation energy for π→π* transition obtained in the present study, 6.96eV, agrees well with the experimental value, 6.7–6.9eV. Calculated excitation energies along with the oscillator strengths clarify that the main excitation in VC is the π→π* excitation. Contrary to the earlier theoretical reports, the results obtained here support that the C–Cl bonddissociation takes place through the nCl-σ*C–Cl state.This study has been supported by the Grant for Creative Scientific Research from the Ministry of Education, Science, Sports, and Culture of Japan