Vibronic spectrum of jet-cooled 2-chloro-5-fluorobenzyl radical: Assignments and substituent effect

We report spectroscopic constants of the jet-cooled 2-chloro-5-fluorobenzyl radical which was generated by corona discharge of precursor 2-chloro-5-fluorotoluene seeded in a large amount of helium carrier gas using a pinhole-type glass nozzle. The visible vibronic emission spectrum was recorded with a long-path monochromator. From an analysis of the spectrum observed, the electronic energy of the D1 → D0 transition and vibrational mode frequencies in the D0 state were determined for the first time by comparing its vibronic data with those of a precursor and ab initio calculation. In addition, the substituent effect on electronic transition energy has been discussed.