Long-lived Electronic Coherences of Molecular Excited States*

Quantum coherence between excited electronic states is a fundamental phenomenon with practical implications for light-initiated processes. Initially excited system can exist in a superposition of multiple states, which introduces interference effects that can be directly probed using present photoionization experiments. For some molecules, multiphoton absorption can be used to prepare coherences that can persist for several hundreds of femtoseconds.

In this work, we use mixed quantum-classical dynamics to explain observation of long-lived coherences in thiophene. We combine the time-dependent configuration interaction method (TDCI) for propagation of the electrons and decoherence-corrected Ehrenfest molecular dynamics with collapse-to-a-block (TAB) to describe the nuclear motion. With these recently developed tools we aim to reconstruct the experiment by directly modeling the pulse excitation and subsequent dynamics of an ensemble of molecules. The results show involvement of low-lying Rydberg states that maintain coherence throughout extensive vibrational motion.