Excited state non-adiabatic dynamics of N-methylpyrrole: A time-resolved photoelectron spectroscopy and quantum dynamics study

The dynamics of N-methylpyrrole following excitation at wavelengths in the range 241.5-217.0 nm were studied using a combination of time-resolved photoelectron spectroscopy (TRPES), ab initio quantum dynamics calculations using the multi-layer multi-configurational time-dependent Hartree method, as well as high-level photoionization cross section calculations. Excitation at 241.5 and 236.2 nm results in population of the A₂(πσ^∗) state, in agreement with previous studies. Excitation at 217.0 nm prepares the previously neglected B₁(π3p_y) Rydberg state, followed by prompt internal conversion to the A₂(πσ^∗) state. In contrast with the photoinduced dynamics of pyrrole, the lifetime of the wavepacket in the A₂(πσ^∗) state was found to vary with excitation wavelength, decreasing by one order of magnitude upon tuning from 241.5 nm to 236.2 nm and by more than three orders of magnitude when excited at 217.0 nm. The order of magnitude difference in lifetimes measured at the longer excitation wavelengths is attributed to vibrational excitation in the A₂(πσ^∗) state, facilitating wavepacket motion around the potential barrier in the N–CH₃ dissociation coordinate