Polarized infrared absorption spectra of matrix-isolated allyl radicals

We have measured the polarized infrared absorption spectrum of the allyl ra dical, CH2CHCH2 ((X) over tilde) (2)A(2), in an argon matrix at 10 K. The e xperimental CH2CHCH2 frequencies (cm(-1)) and polarizations follow: a(1) mo des, 3109, 3052, 3027, 1478, and 1242; b(1) modes, 983, 801, and 510; b(2) modes, 3107, 3020, 1464, 1390, and 1182. Two modes (v(6) and v(18)) are ver y weak and could not be detected; the lowest frequency a, mode (the CH2-CH- CH2 bending mode v(7)) is estimated to be beyond the wavelength range of ou r MCT infrared detector. Infrared absorption spectra of two deuterated isot opomers, CH2CDCH2 and CD2CDCD2, were recorded in order to compare experimen tal frequency shifts with calculated [UB3LYP/6-311-G(d,p)] harmonic frequen cies. Linear dichroism spectra were measured with photooriented samples in order to establish experimental polarizations of most vibrational bands. Tr ue gas-phase vibrational frequencies were estimated by considering the gas- to-matrix shifts and matrix inhomogeneous line broadening. The allyl radica l matrix frequencies listed above are within +/-1% of the gas-phase vibrati onal frequencies. A final experimental set of all the vibrational frequenci es for the allyl radical are recommended. See also: http://ellison.colorado .edu/allyl.