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

J Phys Chem A. 2015 Jun 11;119(23):6099-110. doi: 10.1021/acs.jpca.5b00444. Epub 2015 Mar 25.

Abstract

To study the excited state dynamics between a calcium atom and the CH3F molecule, a Ca···CH3F 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 (1)P1(4s4p) + CH3F allows observing two competitive channels: the direct dissociation and the reactive channel into CaF* + CH3. 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*···FCH3 complex initiates a fast predissociation from a suspended well to two repulsive surfaces that lead either to Ca (1)P1(4s4p) (Ω = 1) + CH3F or to CaF((2)Δ) + CH3.