The Photoelectron Spectroscopy of The Dichoroetylenes: The Geminal Isomer 1,1- Cl2C2H2. An Experimental and Quantum Chemical Study.

This work analyzes the threshold photoelectron spectrum (TPES) and selected Constant Ion State (CIS) spectra of the 1,1-C2H2Cl2 isomer measured using synchrotron radiation. The TPES is compared to the HeI-, NeI- and ArII-photoelectron spectra (PES). In the HeI-PES nine photoelectron bands have been observed at vertical ionization energies of 9.992 eV, 11.652 eV, 12.157 eV, 12.536 eV, 13.633 eV, 14.195 eV, at about 15.9 eV and 16.2 eV and at 18.496 eV successively. For most of these bands the adiabatic ionization energy could be determined and a detailed vibrational analysis of the first four bands is presented. All these bands exhibit an extended vibrational structure. In particular, the ground electronic state and the third excited state display an extended vibrational structure upon excitation by the ArII-resonance line. The assignments of the electronic bands and of the vibrational structure are based on quantum chemical calculations. These allowed us to assign the nine electronic states in terms of ionization and double excitation in a molecular orbital scheme. The good correlation between predicted vibrational wavenumbers and the experimental values allowed us to assign all observed vibrational structures. The CIS spectrum of the eight first electronic states of 1,1-C2H2Cl2+ have also been recorded. Vibrationally resolved CIS spectra of the molecular ion ground state have been obtained and are discussed.