Femtosecond predissociation dynamics of the methyl radical from the 3pz Rydberg state

Abstract

The real time dynamics of electronic predissociation of the CH₃ radical (and its deuterated variant CD₃) from selected vibrational states of the 3p_z Rydberg state have been measured for the first time using a novel methodology based on a femtosecond three-color experiment to generate, two-photon excite and ionize methyl radicals as a function of time in combination with velocity map imaging detection. Subpicosecond lifetimes have been measured, showing a decreasing trend as vibrational excitation in the symmetric stretch and bending umbrella modes increases for both species. High-level ab initio calculations have been carried out in order to elucidate the CH₃ 3p_z predissociation mechanism and support the lifetime measurements. The observed lifetimes are relevant for the understanding of the resonance enhanced multiphoton ionization spectroscopy of this radical.