Capturing and cONtrolling coniCal intErsections in Real Time

Conical intersections (CIs) are regions in the potential energy surface of molecules where different electronic energy levels intersect, leading to the breakdown of the Born-Oppenheimer approximation and promoting non-adiabatic transitions between electronic states. CIs preside over essential ultrafast processes in photobiology, photochemistry, and materials science as they can be viewed as “doorways” through which a photoexcited vibrational wave packet (WP) is efficiently funnelled to a lower-energy electronic state.Despite theoretical predictions, CIs have been experimentally elusive so far, due to the extreme speed of the processes leading to and occurring at the CIs and to the associated large variation in the energetic landscape of the molecule, calling for extreme spectral and temporal resolutions. Leveraging recent experimental advances in the generation of ultrashort soft X-ray pulses and conceptual advances in nonlinear optical spectroscopy, CONCERT aims to: i) directly visualise the very moment in which the molecular WP passes through the CI and the associated quantum mechanical electronic coherences; ii) use this knowledge to control, using tailored light pulses, the WP dynamics in the vicinity of a CI and, ultimately, the outcome and the yield of a photochemical reaction by operating exactly where the fate of the process is decided.CONCERT will have both fundamental and applied impact. On the one hand, it will enable the understanding of the molecular mechanisms driving the passage of a WP through a CI, advancing our knowledge of nature and providing design guidelines for artificial molecular systems that mimic the natural ones. On the other hand, it will offer the ability to control the rates and branching ratios of photochemical processes by manipulating the excited state WP in the critical region that determines its ultimate path, fulfilling the long-held dream of using light as a photonic catalyst to control the outcome of chemical reactions.