15min:

DAIRENE UY, SCOTT DAVIS, DAVID J. NESBITT, JILA, National Institute of Standards and Technology and Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado 80309-0440.

A glow discharge, slit supersonic expansion in conjunction with direct infrared laser absorption have been utilized to record high resolution vibration-rotation spectra of the C₃H₅ allyl radical. The slit supersonic expansion results in efficient rotational cooling (T_rot\leq 20 K),thereby facilitating assignment. Specifically, approximately 50 transitions are assigned for both the in-phase (₁) and out-of-phase (₁₃) CH₂ antisymmetric vibrations. Least squares fits of the transition frequencies to an asymmetric top Hamiltonian provide both ground and excited state rotational constants. While the overall quality of the fits (~ 5× 10^-4 cm^-1) are good, residuals do indicate perturbations in the vibrationally excited state. Due to the high instrumental resolution (slit supersonic Doppler width ~ 70 MHz) spin-rotation broadening is observed in several low J transitions. Small step size (4 MHz) scans over selected transitions coupled with a detailed lineshape analysis indicate a spin-rotation constant \varepsilon_aa of -47(4) MHz.