Reactive and Inelastic Channels in the Ca*center dot center dot center dot FCH3 Transition State: A Simple Branching Mechanism

To study the excited state dynamics between a calcium atom and the CH<inf>3</inf>F molecule, a Ca···CH<inf>3</inf>F 1:1 complex has been prepared by a supersonic expansion with laser ablation of calcium metal in the gas phase. Tunable laser excitation of these complexes in molecular states correlating to Ca ¹P<inf>1</inf>(4s4p) + CH<inf>3</inf>F allows observing two competitive channels: the direct dissociation and the reactive channel into CaF∗ + CH<inf>3</inf>. The translational recoil, as well as the alignment of the fragments Ca∗ and CaF∗ have been analyzed by velocity map imaging and time-of-flight mass spectrometry. This revealed that both the dissociation and reaction processes are quasi direct and are of comparable intensity. We provide a simple interpretation for this process: the electronically excited potential surface of the Ca···FCH<inf>3</inf> complex initiates a fast predissociation from a suspended well to two repulsive surfaces that lead either to Ca ¹P<inf>1</inf>(4s4p) (ω = 1) + CH<inf>3</inf>F or to CaF(²Δ) + CH<inf>3</inf>.