SUBSTITUENT EFFECTS ON GAS-PHASE PHOTODISSOCIATION DYNAMICS - RESONANCE RAMAN-SPECTRA OF ETHYL IODIDE, ISOPROPYL IODIDE, AND TERT-BUTYL IODIDE

We report resonance Raman spectra of photodissociating ethyl, isopropyl, and tert-butyl iodide in the gas phase in order to study the effects that changes in the mass and branching of the alkyl group have on the dissociation. These resonance Raman spectra at 266-nm excitation are compared with preresonant spectra taken with 355-nm excitation and previously published 266-nm spectra of methyl iodide. The dissociation coordinate appears to be primarily in the direction of the C-I stretch motion, but there are significant contributions from bending motions about the alpha-carbon. The bending motions appear to become more important as the alkyl group mass and the branching about the alpha-carbon increase. These gas-phase resonance Raman spectra are compared with similar measurements made in solution. This comparison reveals that overall the short-time dissociation dynamics of the isolated and solvated molecules are similar, but there are some significant differences.