Photochemistry of toluene vapor at 193 nm. Direct measurements of formation of hot toluene and the dissociation rate to benzyl radical

Toluene has been photolyzed with an ArF laser (193 nm) in the gas phase. Time-resolved absorption spectra show that vibrationally hot toluene (S**0) is formed after rapid internal conversion from the S3 state, and then dissociates to benzyl radical. The formation rate of benzyl radical from hot toluene has been measured to be (2.4±0.2)×106 s−1 under collision-free conditions. It has been shown that there are two photodissociation processes to benzyl radical at 193 nm. The major process is efficient internal conversion and formation of hot molecules which is followed by dissociation. The other process is a predissociation. Importance of ‘‘hot’’ intermediates is pointed out in the mechanism of ‘‘photochemical’’ reactions of benzene derivatives.