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The photodissociation of CHBr3 at 193 run has been investigated using photo fragment translational spectroscopy with VUV ionization detection. The only primary process observed was the loss of bromine atom. The translational energy distribution for this channel suggests a direct dissociation from an excited electronic state, and the anisotropy parameter, fJ=O.O, is consistent with a transition dipole moment aligned perpendicular to C 3 v axis. The majority of nascent CHBr2 fragments undergo secondary dissociation via two competing channels. The elimination ofHBr and C-Br bond cleavage in CHBr 2 occur with comparable yields. We also provide ab initio calculations on the relevant photochemical species and RRKM estimates of the product branching ratios that are consistent with the experimental observations.

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Articles you may be interested inPhotodissociation of 1-bromo-2-butene, 4-bromo-1-butene, and cyclopropylmethyl bromide at 234 nm studied using velocity map imaging Translational energy distributions of the products of the 193 and 157 nm photodissociation of chloroethylenes This paper presents product translational energy spectroscopy measurements of the primary photofragmentation channels of 2-chloropropene excited at 193 nm and of the unimolecular dissociation of the 2-propenyl radical. Tunable vacuum ultraviolet ͑VUV͒ photoionization of the products allows us to distinguish between the various product isomers formed in these processes. The data show evidence for three significant primary reaction channels in the dissociation of 2-chloropropene: An excited-state C-Cl fission channel producing fast Cl atoms, a C-Cl fission channel producing slow Cl atoms, and HCl elimination. A minor C-CH 3 fission channel contributes as well. The measured branching of the major primary product channels is: ͓fast C-Cl͔:͓slow C-Cl͔:͓HCl elimination͔ϭ62%:23%:15%. The experiments also allow us to resolve selectively the product branching between the unimolecular dissociation channels of the 2-propenyl radical, a high energy C 3 H 5 isomer; we measure how the branching ratio between the two competing C-H fission channels changes as a function of the radical's internal energy. The data resolve the competition between the unimolecular Hϩallene and Hϩpropyne product channels from the radical with internal energies from 0 to 18 kcal/mol above the Hϩpropyne barrier. We find that the barrier to Hϩallene formation from this high-energy C 3 H 5 radical is higher than the barrier to Hϩpropyne formation, in agreement with recent theoretical calculations but in sharp contrast to that predicted for the most stable C 3 H 5 isomer, the allyl radical. The experiments demonstrate a general technique for selectively forming a particular C n H m isomer dispersed by internal energy due to the primary photolysis, thus allowing us to determine the branching between unimolecular dissociation channels as a function of the selected radical isomer's internal energy.

Photodissociation of ethylene sulfide at 193 nm has been studied using photofragment translational spectroscopy and ab initio theoretical calculations. Tunable synchrotron radiation was used as a universal but selective probe of the reaction products to reveal new aspects of the photodissociation dynamics. The channel giving S + C2H4 was found to be dominated by production of ground-state sulfur atoms (S(3P):S(1D) = 1.44:1), mostly through a spin-forbidden process. The results also suggest the presence of a channel giving S(3P) in conjunction with triplet ethylene C2H4 (3B(1u)) and allow insight into the energy of the latter species near its equilibrium geometry, in which the two methylene groups occupy perpendicular planes. In addition, a channel leading to the production of H2S with C2H2 also has been observed. Our experimental results are supported and elaborated by theoretical calculations.

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The photodissociation dynamics of furan at 193 nm have been studied using photofragment translational spectroscopy with tunable vacuum ultraviolet ͑VUV͒ probe provided by synchrotron radiation on the Chemical Dynamics Beamline at the Advanced Light Source. Three primary channels are observed: HCOϩC 3 H 3 , COϩC 3 H 4 , and H 2 CCOϩC 2 H 2. The evidence suggests that the two closed-shell channels occur on the ground-state potential energy surface ͑PES͒ following internal conversion, while the radical channel likely takes place on an excited PES. All channels exhibit a barrier for dissociation with the acetyleneϩketene channel having the largest value at about 25 kcal/mol. Angular distribution measurements show anisotropy only for the radical channel. These findings are consistent with a rapid excited state dissociation for the radical channel and slow dissociation for the other two pathways. The two ground-state dissociation channels-propyneϩCO and acetyleneϩketene-should be important in the thermal decomposition of furan as was found in pyrolytic studies ͓A.

Tunable synchrotron radiation has been used to probe the dissociation dynamics of ethylene sulfide, providing selective determination of the translational energy distributions of both excited eo) and ground state eP) sulfur atoms, with momentummatching to the ethylene cofragments. The results suggest the presence of a channel giving seP) in conjunction with triplet ethylene C2~ eB tu). and. allow for the first experimental measure of the energy of the latter species near the equilibrium geometry, in which the two methyene groups occupy perpendicular planes.