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 A(2)(pi sigma*) state, in agreement with previous studies. Excitation at 217.0 nm prepares the previously neglected B-1(pi 3p(y)) Rydberg state, followed by prompt internal conversion to the A(2)(pi sigma*) state. In contrast with the photoinduced dynamics of pyrrole, the lifetime of the wavepacket in the A(2)(pi sigma*) 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 A(2)(pi sigma*) state, facilitating wavepacket motion around the potential barrier in the N-CH3 dissociation coordinate. (C) 2016 AIP Publishing LLC.