Spectroscopic identification of jet-cooled 2,4-dichlorobenzyl radicals generated by corona discharge

Vibronically excited but jet-cooled 2,4-dichlorobenzyl radical was generated from the precursor 2,4-dichlorotoluene using a pinhole-type glass nozzle designed for the dual purposes of corona discharge and supersonic jet expansion. From the analysis of the visible vibronic emission spectra of the jet-cooled 2,4-dichlorobenzyl radical observed, substituent effect of two Cl atoms on electronic transition energy was rationalized. In addition, we determined the electronic energy of the D1 → D0 transition and vibrational mode frequencies in the D0 state of the jet-cooled 2,4-dichlorobenzyl radical using the results of an ab initio calculation and known spectroscopic data of the precursor.