Hexamethylcyclopentadiene: time-resolved photoelectron spectroscopy and ab initio multiple spawning simulations.

Area of Science:

• Physical Chemistry
• Quantum Chemistry
• Spectroscopy

Background:

• Ultrafast light-induced processes in molecules require integrated experimental and theoretical methods.
• Reproducing experimental observables in theory is crucial for advancing molecular dynamics understanding.

Purpose of the Study:

• To disentangle the relationship between spectral delays and excited-state depopulation in molecular response to light.
• To establish a benchmark comparison between time-resolved photoelectron spectroscopy (TRPES) and ab initio multiple spawning (AIMS) simulations.

Main Methods:

• Utilized a joint approach combining TRPES experiments with ab initio multiple spawning (AIMS) simulations at the MS-MR-CASPT2 level.
• Employed hexamethylcyclopentadiene as a benchmark molecule, with simplified methyl groups for simulations.
• Calculated TRPES spectra from dynamics simulations to analyze spectral delays and induction times.

Main Results:

• Observed an unprecedented spectral delay of (310 ± 20) fs in TRPES experiments for hexamethylcyclopentadiene.
• AIMS simulations revealed an induction time of (108 ± 10) fs, directly linked to torsional motion towards the ground state seam.
• Established a clear connection between spectral delay and excited-state depopulation dynamics.

Conclusions:

• The combined TRPES and AIMS approach is a powerful tool for understanding ultrafast excited-state dynamics.
• The findings support the general validity of the observed phenomena for polyenes.
• This work elucidates the interplay between spectral features and molecular dynamics following photoexcitation.