Electronic Spectra of Tetrafluorobenzene Cations Produced by Pulsed Glow Discharge in a Supersonic Free Jet

Abstract

Abstract Cold ions of tetrafluorobenzene isomers were produced by pulsed glow discharge in a supersonic free jet and the electronic spectra due to D2–D0 transitions were observed. The vibrational frequencies of the ions were determined for the ground and electronically excited states through observations of the fluorescence excitation and dispersed fluorescence spectra under collision-free conditions. The vibronic bands observed in the spectra were assigned to totally symmetric vibrations. The difference in the vibrational frequencies between the ion and neutral molecules is very small in spite of the ejection of an electron from the π orbital. A very small frequency change is observed in the electronic excited state of the ions. The frequencies observed for the ions show that the bonding π orbitals are less effective for chemical bonds of the molecules. The electronic spectra of the 1,2,4,5-tetrafluorobenzene cation, whose neutral parent molecule is distorted in the S1 state along the fluorine-wagging normal mode, gave no sign of such a structural change in the electronic excited D2 state.