Dynamics of harpooning studied by transition state spectroscopy. Part III. Li...FCH3.

The Van der Waals complex Li...FCH3 has been formed in a crossed molecular beam apparatus. The transition state (TS) for the reaction Li*(2p 2P) + FCH3-->LiF + CH3 was accessed at various configurations by laser-excitation of the Li...FCH3 complex by tunable visible radiation, lambda 1. Photoinduced depletion of the complex by excitation to this TS was found to occur across a broad range of lambda 1 from 570 to 850 nm. This 'action spectrum' consisted of two broad regions located to either side of the atomic transition line of Li (2p 2P<--2s 2S). The first region, between 700 and 850 nm, was dominated by sharp maxima in the depletion intensity. A broad peak with weakly-resolved structure characterized the second region, between 570 and 680 nm. These findings were interpreted by means of high-level ab initio calculations of the potential-energy surfaces in the TS region. The peaks in the photodepletion spectrum were assigned to specific electronic transitions, their shapes and intensities being explained in terms of calculated transition-dipole moments and rovibrational wavefunctions.