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, λ₁. Photoinduced depletion of the complex by excitation to this TS was found to occur across a broad range of λ₁ 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.