Spectroscopy of the vinyl radical

The Spectrum of the Vinyl radical (C2H3) A&d5;2A'' ←X2A' &d5; transition has been measured between 530 and 385 nm by using cavity-ringdown spectroscopy. For the lowest energy vibrational bands, the rotational constants, A, B and C, and the linewidth were optimized by calculating the spectrum of this asymmetric top molecule with a computer program to get the best agreement between the calculated spectrum and the experimentally measured one. From the best-fit spectra, information on the geometry and the lifetime of the vinyl radical in the vibrationless level in the excited electronic state was obtained. From the change in the rotational constants and the linewidth with increasing vibrational excitation, information on the deformation and decrease in lifetime of the molecule in the excited electronic state with increasing vibrational excitation has been determined. In this way, we have obtained structural and dynamic information for several low-lying vibrational levels in the excited electronic state. With higher vibrational excitation, the calculated spectra no longer match the experimental spectra, and the linewidth becomes very broad, possibly indicating new dynamics above a threshold energy in the excited electronic state.