Photodissociation of the allyl radical, CH2CHCH2, has been studied using the method of molecular beam photofragment translational spectroscopy following excitation to the (C) over tilde(2 B-2(1)) and (A) over tilde(1 B-2(1)) states by 248 and 351 nm photons. Two different primary channels have been detected following 248 nm excitation: H-atom loss (84%) and CH3 elimination (16%). From the product translational energy distribution and polarization dependence studies, dissociation processes from the ground-state C3H5 potential energy surface are inferred for both wavelengths. At 248 nm there may also be a contribution to the H-atom loss channel from predissociation by a higher electronically excited state. Rice-Ramsperger-Kassel-Marcus (RRKM) calculations show that the formation of cyclopropene is not important, while formation of allene and methylacetylene from dissociation of 1- and 2-propenyl radicals are important reaction pathways at both wavelengths. Translational energy distributions peaking well away from zero provide evidence for CH3 elimination directly from an allylic structure through a four-member cyclic transition state. (C) 1998 American Institute of Physics. [S0021-9606(98)02137-0]

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The photodissociation of ozone has been studied at 193 nm using high resolution photofragment translational spectroscopy. The results show six distinct peaks in the time-of-flight spectra for the O2 product and its momentum-matched O atom counterpart. The translational energy distributions determined from the time-of-flight spectra reveal the production of a range of electronic states of the photofragments. The product electronic states were identified based on the translational energy distributions, with the aid of state-resolved imaging experiments by Houston and co-workers. The results reveal the production of a substantial yield of highly excited triplet states of O2, recently suggested to play an important role in the stratospheric ozone balance. In addition, peaks corresponding to O2(a 1Δg) and O2(b 1Σg+) were observed, the latter confirming a previous report [A. A. Turnipseed et al., J. Chem. Phys. 95, 3244 (1991)]. Evidence was seen for a small contribution from the triple dissociation O3→3O(3P), and insight into the dissociation dynamics for this process was inferred from the translational energy distributions. Branching fractions and angular distributions were measured for all channels. The latter were found in general to yield negative β parameters, in contrast to what is seen at longer wavelengths.