The ability to probe energy flow in molecules, following the absorption of ultraviolet light, is crucial to unraveling photophysical phenomena. Here we excite a coherent superposition of vibrational states in the first excited electronic state (${\mathit{S}}_1$) in catechol, resulting in a vibrational wave packet. The observed quantum beats, assigned to superpositions of the low-frequency, and strongly mixed, O–H torsional mode ${\tau }_2$, elegantly demonstrate how changes in geometry upon photoionization from the $S_1$ state to the ground state of the cation ($D_0$) enables one to probe energy flow at the very early stages of photoexcitation in this biological chromophore.

• Received 4 February 2015

DOI:https://doi.org/10.1103/PhysRevLett.114.233001

This article is available under the terms of the Creative Commons Attribution 3.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.

© 2015 American Physical Society