Journal of Physical Chemistry, Vol.100, No.19, 7772-7777, 1996
Resonance Raman-Spectroscopy of the 1-Methylallyl Radical
The first vibrational spectrum of the 1-methylallyl radical is detected using resonance Raman spectroscopy with excitation from 237 to 232 nm. The vibrational frequencies of five symmetric fundamentals, the H3C-CCC bend, the CCC bend, the H3C-C stretch, the C-H in plane bend, and the CH2 scissors, of the 1-methylallyl radical are reported. The even overtones of the CH3 torsion, the C-H out of plane bend, the H3C-CCC bend, and the CCC bend are identified. The vibrational assignments of the resonance Raman spectra are based upon comparison with calculated vibrational frequencies generated by UHF method using a 6-31G* basis set and experimental values for the allyl radical, the beta-methylallyl radical, and similar molecules. Excitation at 236.05 and 234.95 nm yields significant resonance enhancement of overtone and combination bands associated with the H3C-CCC bend and CCC bend, respectively. The variation of intensities in the Raman spectra with excitation wavelength yields excited state vibrational frequencies for the H3C-CCC bend and CCC symmetric bend of 305 and 502 cm(-1), respectively. Examination of the observed intensity patterns in the resonance Raman spectra indicates that the initial excited state dynamics of the 1-methylallyl radical are dominated by bending motions of the carbon chain.