ON THE FORMATION AND VIBRONIC SPECTROSCOPY OF ALPHA-HALOBENZYL RADICALS IN A SUPERSONIC EXPANSION

alpha-halobenzyl radicals, such as C6H5CHCl, C6H5CHBr, and C6H5CCl2, a long with C6H5CH2, are generated by pyrolysis and photolysis methods. The mechanism of the formation of the alpha-halobenzyl radicals in a p yrolysis nozzle is analyzed. Secondary reactions play an important rol e in the pyrolysis process. Spectra of these supersonic jet cooled rad icals are detected by laser induced fluorescence and multiphoton ioniz ation techniques in the 21 200-23 500 cm(-1) range. Assignment of impo rtant vibronic bands of the alpha-halobenzyl radicals is made by compa ring their spectra to that of the benzyl radical and by employing rota tional contour and vibrational mode analyses and ab initio calculation s. The similarity between the vibronic structure of the benzyl radical and alpha-halobenzyl radicals suggests a similar vibronic coupling sc heme for them. Substitution of halogen atoms on the methylene group of the benzyl radical has only a modest affect on the vibronic transitio ns studied. (C) 1997 American Institute of Physics.