Ultraviolet photodissociation of furan probed by tunable synchrotron radiation

The photodissociation dynamics of furan at 193 nm have been studied using p hotofragment translational spectroscopy with tunable vacuum ultraviolet (VU V) probe provided by synchrotron radiation on the Chemical Dynamics Beamlin e at the Advanced Light Source. Three primary channels are observed: HCO+C3 H3, CO+C3H4, and H2CCO+C2H2. The evidence suggests that the two closed-shel l channels occur on the ground-state potential energy surface (PES) followi ng internal conversion, while the radical channel likely takes place on an excited PES. All channels exhibit a barrier for dissociation with the acety lene+ketene channel having the largest value at about 25 kcal/mol. Angular distribution measurements show anisotropy only for the radical channel. The se findings are consistent with a rapid excited state dissociation for the radical channel and slow dissociation for the other two pathways. The two g round-state dissociation channels-propyne+CO and acetylene+ketene-should be important in the thermal decomposition of furan as was found in pyrolytic studies [A. Lifshitz, M. Bidani, and S. Bidani, J. Phys. Chem. 90, 5373 (19 86)] and theoretical investigations [R. Liu, X. Zhou, and L. Zhai, J. Compu t. Chem. 19, 240 (1998)]. (C) 1999 American Institute of Physics. [S0021-96 06(99)01625-6].