Methylsulfonyl radical unimolecular dissociation studied by deep-UV ultrafast photoionization spectroscopy

The secondary dissociation dynamics of the methylsulfonyl radical following the photodissociation near 193 nm of methylsulfonyl chloride and methylsul fonyl ethanol has been studied using femtosecond mass-resolved photoionizat ion spectroscopy. The primary dissociation is instrument-limited (<200 fs) for both precursors. The methylsulfonyl unimolecular dissociation is measur ed to have a lifetime of 0.34 ps with complete secondary dissociation follo wing methylsulfonyl chloride photolysis. For the case of methylsulfonyl eth anol, the measured lifetime is 1.1 ps and <similar to>40% of the radical re mains undissociated for the 18 ps duration of the experiment. We have succe ssfully modeled the experimental results assuming an impulsive dissociation process to yield the internal energy distributions in the primary photopro ducts and RRKM calculations based on structures and energetics of the methy lsulfonyl radical obtained from the literature.