Photodissociation dynamics of ethanol at 193.3 nm: The H-atom channel and ethoxy vibrational distribution

193.3 nm photodissociation of jet-cooled C2H5OH and C2H5OD has been studied by using the high-n Rydberg-atom time-of-flight technique. Isotope labeling study shows that the H-atom photofragment is produced preferentially from O-H bond fission upon ultraviolet excitation. Center-of-mass (c.m.) translational energy distribution of the H(D) atom and ethoxy radical photofragments has been obtained. Average c.m. product translational energy is large, with < E-T>=0.84E(avail) for H+C2H5O and < E-T>=0.80E(avail) for D+C2H5O, respectively. Maximum c.m. translational energy release yields an upper limit of the bond dissociation energy: D-0(C2H5O-H)=103.7 +/- 0.5 kcal/mol and D-0(C2H5O-D)=105.9 +/- 0.5 kcal/mol. The c.m. translational energy distribution of the C2H5O+H products reveals extensive C-O stretch and modest C-C-O bending excitation in the C2H5O radical, which can be rationalized by the geometric change in going from the parent molecule to the excited surface and then to the ethoxy radical product, and can be simulated by a simple Franck-Condon model. H-atom product angular distribution is anisotropic (with beta approximate to-0.9), indicating a perpendicular electronic transition ((A) over tilde (1)A"<--(X) over tilde (1)A') at 193.3 nm and a short excited-state lifetime (less than a rotational period). The obtained dynamic information implies that the C2H5O+H channel in 193.3 nm photodissociation of ethanol occurs via a prompt dissociation process and on a repulsive excited-state surface, and the ethoxy product vibrational distribution further reveals the detailed multidimensional features of this excited A (1)A(') potential energy surface. Secondary photodissociation of the ethoxy radical has been observed and is briefly discussed. (C) 1999 American Institute of Physics. [S0021-9606(99)01838-3].