HIGH-RESOLUTION INFRARED-SPECTROSCOPY OF JET-COOLED ALLYL RADICAL (CH2-CH-CH2) - IN-PHASE (NU(1)) AND OUT-OF-PHASE (NU(13)) ANTISYMMETRIC CH2 STRETCHING VIBRATIONS

High-resolution infrared spectra of jet-cooled allyl (CH2-CH-CH2) radi cal in the CH2 stretching region are obtained in a slit jet discharge spectrometer. Over 200 transitions are observed in the 3100-3140 cm(-1 ) region, which have been rigorously assigned to ''in-phase'' (v(1)) a nd ''out-of-phase'' (v(13)) coupling of antisymmetric CH stretch excit ations on each of the equivalent CH2 subunits. Origins for the two ban ds are determined to be 3113.98 488(89) cm(-1) (v(1)) and 3110.59 857( 36) cm(-1) (v(13)), respectively. The data are reasonably well fit to semirigid asymmetric rotor behavior for the K-a less than or equal to 2 levels populated in the slit jet at T-rot approximate to 20 K, thoug h not to within the experimental precision, which provides some indica tion of perturbations in the upper states. The sign and magnitude of t he +3.4 cm(-1) splitting between ''in-phase'' and ''out-of-phase'' exc itations are in good qualitative agreement with a simple electrostatic model of dipole-dipole coupling between the two ''local mode'' CH2 gr oups. Due to sub-Doppler resolution (Delta v approximate to 70 MHz) in the slit jet expansion, quantum-state-dependent excess broadening of the rovibrational transitions is observed, which can be ascribed to sp in-rotation interactions. Based on a least squares analysis of the hig h-resolution line shapes, the data are consistent with a spin rotation constant of epsilon(aa) approximate to -67(25) MHz. (C) 1998 American Institute of Physics. [S0021-9606(98)01142-8].