MILLIMETER-WAVE SPECTROSCOPY OF THE HCCCO AND DCCCO RADICAS

Abstract

1. Z.A TomaxiEcA and G.E. Suxeria, J. Phys. Chem. 95 , 6905-6908(1991). 2. R.D. Brown, R. Champion, P.S. Elmes, and P.D. Godfrey, J. Am. Chem. Soc. 107 , 4109-4112(1985). 3. Y. Endo and E. Hirota, J. Chem. Phys. 86 , 4319-4326 (1987).Author Institution: Harvard-Smitsonian Center for Astrophysics, and Department of Chemistry, Harvard University; Herzberg Institute of Astrophysics, National Research Council; Division of Applied Sciences, Harvard University; Division of Applied Sciences, Harvard-Smithsonian Center for AstrophysicsOver 300 rotational transitions of the free radicals HCCCO AND DCCCO between 80 and 400 GHz have been observed by millimeter-wave glow discharge spectroscopy. Analysis of ground state energy levels of $N = 8 = 40$ and $Ka = 0-3$ using the S-reduced asymmetric top effective Humiltonian, including treatment of a reasonant spin-rotation perturbation, confirms the qualitative ab initio result that HCCCO and DCCCO have highly prolate bent chain $structures^{1}$. However, the rotational constants are reproduced with better precision by removing one hydrogen from the experimental $H_{2}CCCO$ $structure,^{2}$ implying that HCCCO is more bent than predicted. The rotation and spin-rotation constants indicate that the Renner-Teller effect in this system is stronger than in $HCCCO_{1}^{3}$ and the high degree of distortion is evidence for substantial coupling between bending vibration and rotation about the a-axis. Analysis of the moments of inertia of the two isotopomers yield the a-- and b--axis coordinates of the hydrogen atom and a -- and b--axis moments of inertia for the CCCO subunit in the vibrationally averaged structure