We have measured the polarized infrared absorption spectrum of the allyl radical, CH2CHCH2 () 2A2, in an argon matrix at 10 K. The experimental CH2CHCH2 frequencies (cm-1) and polarizations follow: a1 modes, 3109, 3052, 3027, 1478, and 1242; b1 modes, 983, 801, and 510; b2 modes, 3107, 3020, 1464, 1390, and 1182. Two modes (?6 and ?18) are very weak and could not be detected; the lowest frequency a1 mode (the CH2?CH?CH2 bending mode ?7) is estimated to be beyond the wavelength range of our MCT infrared detector. Infrared absorption spectra of two deuterated isotopomers, CH2CDCH2 and CD2CDCD2, were recorded in order to compare experimental frequency shifts with calculated [UB3LYP/6-311-G(d,p)] harmonic frequencies. Linear dichroism spectra were measured with photooriented samples in order to establish experimental polarizations of most vibrational bands. True gas-phase vibrational frequencies were estimated by considering the gas-to-matrix shifts and matrix inhomogeneous line broadening. The allyl radical matrix frequencies listed above are within ±1% of the gas-phase vibrational frequencies. A final experimental set of all the vibrational frequencies for the allyl radical are recommended. See also: http://ellison.colorado.edu/allyl.
