Photofragment translational spectroscopy was used to study the photodissociation dynamics of the phenyl radical C(6)H(5) at 248 and 193 nm. At 248 nm, the only dissociation products observed were from H atom loss, attributed primarily to H+o-C(6)H(4) (ortho-benzyne). The observed translational energy distribution was consistent with statistical decay on the ground state surface. At 193 nm, dissociation to H+C(6)H(4) and C(4)H(3)+C(2)H(2) was observed. The C(6)H(4) fragment can be either o-C(6)H(4) or l-C(6)H(4) resulting from decyclization of the phenyl ring. The C(4)H(3)+C(2)H(2) products dominate over the two H loss channels. Attempts to reproduce the observed branching ratio by assuming ground state dynamics were unsuccessful. However, these calculations assumed that the C(4)H(3) fragment was n-C(4)H(3), and better agreement would be expected if the lower energy i-C(4)H(3)+C(2)H(2) channel were included.

We have recorded high resolution, partially rotationally resolved, jet-cooled cavity ringdown spectra of the origin band of the A-X electronic transition of both the G and T conformers of the perproteo and perdeutero isotopologues of the ethyl peroxy radical, C(2)H(5)O(2). This transition, located in the near infrared, was studied using a narrow band laser source (< or approximately 250 MHz) and a supersonic slit-jet expansion coupled with an electric discharge allowing us to obtain rotational temperatures of about 15 K. All four spectra have been successfully simulated using an evolutionary algorithm approach with a Hamiltonian including rotational and spin-rotational terms. Excellent agreement with the experimental spectra was obtained by fitting seven molecular parameters in each ground and the first excited electronic states as well as the band origin of the electronic transition. This analysis unambiguously confirms the assignment of the lower frequency origin band to the G conformer and the higher frequency one to the T conformer.

The photodissociation dynamics of the tert-butyl radical (t-C(4)H(9)) were investigated using photofragment translational spectroscopy. The tert-butyl radical was produced from flash pyrolysis of azo-tert-butane and dissociated at 248 nm. Two distinct channels of approximately equal importance were identified: dissociation to H + 2-methylpropene, and CH(3) + dimethylcarbene. Neither the translational energy distributions that describe these two channels nor the product branching ratio are consistent with statistical dissociation on the ground state, and instead favor a mechanism taking place on excited state surfaces.