Hexamethylcyclopentadiene: time-resolved photoelectron spectroscopy and ab initio multiple spawning simulationsElectronic supplementary information (ESI) available. See DOI: 10.1039/c4cp00977k

• Main Authors: Wolf, T. J. A, Kuhlman, T. S, Schalk, O, Martínez, T. J, Møller, K. B, Stolow, A, Unterreiner, A.-N
• Format: Journal Article
• Language: English
• Published: 21.05.2014
• ISSN: 1463-9076; 1463-9084
• DOI: 10.1039/c4cp00977k

Progress in our understanding of ultrafast light-induced processes in molecules is best achieved through a close combination of experimental and theoretical approaches. Direct comparison is obtained if theory is able to directly reproduce experimental observables. Here, we present a joint approach comparing time-resolved photoelectron spectroscopy (TRPES) with ab initio multiple spawning (AIMS) simulations on the MS-MR-CASPT2 level of theory. We disentangle the relationship between two phenomena that dominate the immediate molecular response upon light absorption: a spectrally dependent delay of the photoelectron signal and an induction time prior to excited state depopulation in dynamics simulations. As a benchmark molecule, we have chosen hexamethylcyclopentadiene, which shows an unprecedentedly large spectral delay of (310 ± 20) fs in TRPES experiments. For the dynamics simulations, methyl groups were replaced by "hydrogen atoms" having mass 15 and TRPES spectra were calculated. These showed an induction time of (108 ± 10) fs which could directly be assigned to progress along a torsional mode leading to the intersection seam with the molecular ground state. In a stepladder-type approach, the close connection between the two phenomena could be elucidated, allowing for a comparison with other polyenes and supporting the general validity of this finding for their excited state dynamics. Thus, the combination of TRPES and AIMS proves to be a powerful tool for a thorough understanding of ultrafast excited state dynamics in polyenes. Time-resolved photoelectron spectroscopy and ab initio multiple spawning dynamical simulations of hexamethylcyclopentadiene reveal wavepacket evolution in a distinct degree of freedom.