Imaging conical intersection dynamics during azobenzene photoisomerization by ultrafast X-ray diffraction
Daniel Keefer, Flavia Aleotti, Jérémy R. Rouxel, Francesco Segatta, Bing Gu, Artur Nenov, Marco Garavelli, Shaul Mukamel
Abstract
Significance Vibronic coherences are unique features that emerge in the decisive moments of photochemistry and photophysics. Here we demonstrate how X-ray diffraction can access fundamental information about these coherences. This is enabled by recent developments at free-electron lasers, working toward temporal resolution and single-molecule accessibility of scattering-based measurements. Time-resolved diffraction patterns of the isomerization of azobenzene are simulated. The process is monitored in time via the momentum-space signal, with a special focus on the mixed elastic/inelastic scattering from coherences. We give practical ideas on how this relatively weak contribution to the signal can potentially be retrieved. A direct connection to the real-space movie of the conical intersection dynamics is made, enabling the observation of quantum coherences that direct chemical processes.