Knowledge Bank

The first resonance Raman spectra of the allyl radical have been recorded. The structure and bonding of the allyl radical is of theoretical interest because it is the simplest delocalized pi electron system. The radical is also of interest as a possible combustion intermediate. The gas phase allyl radical was produced by photolysis of allyl iodide and allyl bromide with the fourth and fifth harmonic of the Nd:YAG laser. The output of a DCM dye laser was frequency tripled to provide tuneable for ultraviolet Raman excitation. The probe laser was tuned to the allyl radical $X\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}B1-B\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}B1$ transition at 223 nm. The Raman scattered light was collected in standard backscatter geometry by a 2 inch $f/0.67$ spherical mirror and focussed onto the slits of a 1.0 meter Czerny-Turner monochromator. Spectra of the gas phase radical were recorded using blind photomultiplier tube and gated integrator. The observed spectrum is comprised of four totally symmetric vibrations and several overtones. The observed frequencies will be compared to the theoretical predictions and data derived from infrared matrix isolation and multiphoton ionization methods. Vibrational relaxation of the allyl radical in different buffer gases will also be presented.