Time-resolved photoelectron spectroscopy of the CH3I B1E 6s [2] state

Abstract

The predissociation dynamics of the vibrationless level of the 6s (B ²E) Rydberg state of CH₃I was studied by femtosecond-resolved velocity map imaging of photoelectrons. By monitoring the decay of the CH₃I⁺ produced by photoionizing the B state, the predissociation lifetime was measured to be 1310 ± 70 fs. Photoelectron spectra were recorded as a function of the excitation scheme (one or two photons to the B state), and as a function of the ionizing wavelength. All of these photoelectron spectra show a simple time dependence that is consistent with the decay time of the CH₃I⁺ ion signal. The photoelectron angular distributions for the ionization of the B state depend on the excitation scheme and the ionizing wavelength, and show a strong dependence on the vibrational modes excited in the resulting CH₃I⁺. At long delays, the photoelectron spectra are characterized by photoionization of the I(²P_1/2) fragment formed by predissociation of the B state.