The Vacuum UV Photoabsorption Spectrum of the Geminal Dichloroethylene (1,1-C2H2Cl2) in the 5-20 eV Range. A Vibrational Analysis of the Valence and Rydberg States.

The vacuum UV photoabsorption spectrum of 1,1-C2H2Cl2 is presented and discussed in detail in the 6 - 20 eV photon energy range. The broad band observed at 6.488 eV includes the 2b1()→σ*, 2b1()→* valence transitions and the 2b1()→3s Rydberg transitions. A quantum chemical calculation analysis is proposed and applied to the intertwined vibrational structure belonging to these transitions. For the →σ* and →* transitions short vibrational progressions are observed, analyzed and tentatively assigned. The →3s Rydberg transition is characterized by a single progression starting at 6.746 eV. The fine structure observed between 7.5 eV and 10.1 eV has been analyzed in terms of vibronic transitions to ns- (δ= 0.89), np- (δ= 0.59 and 0.37) and nd-type (δ= 0.16) Rydberg states all converging to the 1,1-C2H2Cl2+( 2B1) ionic ground state. The vibrational structure analysis excitation leads to the following wavenumbers: ω2≈ 1310 cm-1 (162 meV), ω4≈ 650 cm-1 (81 meV) and ω5≈ 290 cm-1 (37 meV). These modes can be assigned to the C=C stretching, to the symmetric C-Cl stretching and to the symmetric Cl-C-Cl bending vibrations respectively. By the same way, eight other Rydberg states were analyzed. For the first time the vacuum UV spectrum of 1,1-C2H2Cl2 has been recorded in the 10 eV-20 eV range, revealing intense broad bands which are assigned to transitions to Rydberg states converging to excited states of 1,1-C2H2Cl2+. Assignments are also proposed for the vibrational excitations observed in this range.