PHOTODISSOCIATION OF TETRAMETHYLENE SULFOXIDE AT 193 AND 248 NM IN THE GAS-PHASE

The 193 and 248 nm photodissociation of tetramethylene sulfoxide (TMSO ) in the gas phase has been investigated by using laser spectroscopic techniques. The vibrational state distributions of the nascent SO(X(3) Sigma(-)) photofragment following irradiation at 193 and 248 nm have been measured by using laser-induced fluorescence (LIF) spectroscopy o n the B-3 Sigma(-)-X(3) Sigma(-) transition. These vibrational state d istributions can be characterized as Boltzmann with vibrational temper atures of 1250 +/- 60 and 1220 +/- 60 K for the 193 and 248 nm photoly ses, respectively. Assuming that the SO photofragment is produced in c oncert with a 1,4-tetramethylene diradical, the vibrational state dist ribution obtained in the 193 nm photolysis agrees well with an energy disposal model, in which the full reaction exoergicity is statisticall y partitioned among all the products' degrees of freedom. The quantum yield for SO(X(3) Sigma(-)) production at 193 nm, Phi(SO)(193) = 0.47 +/- 0.20, has been obtained by comparison with SO2 photolysis. For the 248 nm photodissociation, the experimentally obtained vibrational sta te distribution can be best described by a variant statistical model a ssuming three-body fragmentation; i.e. the products are an SO fragment and two ethylene molecules. The quantum yield for SO(X(3) Sigma(-)) p roduction at 248 nm is Phi(SO)(248) = 0.44 +/- 0.10. The OH photofragm ent has been detected during both the 193 and 248 nm photolyses of TMS O. The rotational state distributions of the OH(X(2)II,v''=0) fragment have been determined by LIF spectroscopy using the A(2) Sigma-X(2)II transition. The hydroxyl rotational temperatures can be characterized as 600 +/- 50 and 510 +/- 40 K following photolysis of TMSO at 193 and 248 nm, respectively. Mechanisms for the production of both SO and OH are discussed.