			15min:

SPECTROSCOPY AND DISSOCIATION DYNAMICS OF THE 1-METHYLALLYL RADICAL .

M. GASSER, J. A. FREY, J. M. HOSTETTLER AND A. BACH, Laboratorium für Organische Chemie, ETH Zürich, CH-8093, Switzerland.

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The A leftarrow X band system of jet-cooled 1-methylallyl radical (C₄H₇) was observed for the first time using resonance-enhanced multiphoton ionization combined with electronic ground state depletion spectroscopy. Analysis of the vibronic structure reveals transitions to the non-planar A valence excited state with an electronic origin for the Z-isomer of 1-methylallyl at 23~979~cm^-1.

Time- and frequency-resolved photoionization of the hydrogen atom product from electronically excited 1-methylallyl radical and its isotopologue CH₃C₃D₄ provides information on the dissociation dynamics. The measured dissociation rates and kinetic energy release combined with results from high level ab initio calculations suggests unimolecular decompostion to 1,3-butadiene and hydrogen with no evidence for nonstatistical behavior in dissociation.