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 D-1 -> D-0 transition and vibrational mode frequencies in the D-0 state of the jet-cooled 2,4-dichlorobenzyl radical using the results of an ab initio calculation and known spectroscopic data of the precursor. (c) 2012 Elsevier B.V. All rights reserved.