UV ABSORPTION-SPECTRA AND FORMATION RATES OF STILBENE IN THE HIGH-TEMPERATURE KINETICS OF BENZYL RADICALS

UV absorption coefficients in the gas phase of trans- and cis-stilbene in the range 270-360 nm are determined between 300 and 1500 K employi ng static cells and shock waves. By means of these spectroscopic data, the rate of stilbene formation in benzyl-containing reaction mixtures between 1000 and 1300 K can be analyzed quantitatively. The ''stilben e pathway'' in benzyl pyrolysis is shown to involve dibenzyl formation and the bimolecular abstraction reaction benzyl + dibenzyl --> toluen e + C6H5CHCH2C6H5 which is followed by fragmentation of C6C5CHCH2C6H5 to stilbene and H, with initial formation of equal amounts of trans- a nd cis-stilbene before thermal Isomerization. A rate constant of the r eaction of k = (4 +/- 2) 10(11) cm(3) mol(-1) s(-1) was determined at 1200-1300 K.