Nanosecond and femtosecond probing of the dynamics of the UV-photodissociation of perfluoroethyliodide C2F5I

Abstract

The ns photodissociation of perfluoroethyliodide C2F5I at 266 nm has been studied by using the resonant two-photon ionization (R2PI) technique. Recoil anisotropy parameters as well as average translational energy of the I atoms in the fine structure states P1/22 and P3/22 have been determined. The main contribution (99%) to the absorption at 266 nm was found to be caused by a parallel transition to the Q03 state which gives mainly excited-state atoms I(2P1/2). The ground-state atoms I(2P3/2) were found to appear mainly (88%) from the primarily excited Q03 state via curve-crossing Q03–Q11 and to a lesser extent (12%) from direct absorption by a perpendicular transition to the Q11 and Q13 states. The fs pump–dump technique in combination with ns R2PI probing of the fragments I(2P1/2) and I(2P3/2) and time-of-flight mass spectrometry have been applied to probe the early stage dynamics of the C2F5I molecule on the excited state Q03 potential energy surface (PES). The evolution time of the excited molecule to the point where the energy gap between the excited state Q03 and the ground-state potential energy surfaces drops to a value of about 12 440 cm−1 was found to be 52±13 fs. This time corresponds to about 0.8 Å extension of the C–I bond distance. The molecular dynamics simulation with DFT calculated ground-state PES and Q03 PES with the shape calculated for methyl iodide found in the literature gives reasonable agreement with the experimental result for the evolution time.