Spectroscopy and Dynamics of Transient Species, the Vinyl Radical and Highly Vibrationally Excited Acetylene

Time-resolved Fourier transform infra-red spectroscopy has been employed to identify vibrational modes of several transient molecular and radical species. IR emission from the vinyl radical generated by five different precursor molecules utilizing different dissociation pathways has been observed. An analytical method, two-dimensional cross spectral correlation, has been employed to verify the low energy bending modes of the vinyl radical as well as one stretching mode. Isotopic substitution has allowed several bending modes to be compared to their non-isotopically substituted analog. Highly vibrationally excited acetylene has also been generated via photochemical reaction. IR emission is modeled according to known harmonic and anharmonic terms of the linear ground electronic state of acetylene. An unexpectedly strong combination band is found in the modeling. Through collisionally induced vibrational energy transfer, energy transfer rates, collisional mass dependence, and the vibrational energy content of acetylene can be obtained. The production of highly vibrationally excited acetylene has presented the opportunity to study a short lived isomer of acetylene, vinylidene. The influence of vinylidene on acetylene is observed in the energy transfer rates at high energy. An enhancement in the energy transfer rate is observed above the acetylene-vinylidene isomerization barrier. An energy transfer model is used to verify this observation. A theoretical model is postulated which involves a mixing of vibrational states of acetylene and vinylidene above the isomerization barrier thus accounting for the enhancement of the energy transfer rate at high energies. Another method involving collisions between translationally hot hydrogen atoms and room temperature acetylene molecules generate a significant amount of vibrationally hot acetylene. Possible mechanisms are proposed and tested via isotopic substitution. A mechanism proceeding through a short lived vinyl intermediate dissociating to form a highly vibrationally excited acetylene molecule was found. A combined statistical/impulsive model and classical trajectory calculation confirm the production of a short lived vinyl radical intermediate.