Simulation of time-resolved site-selective X-ray spectroscopy tracing nonadiabatic dynamics in <i>meta</i> -methylbenzophenone

Benzophenone and its derivatives are important diaryl ketone building blocks that have applications ranging from UV blockers to organic optoelectronics. This class of substances exhibits efficient intersystem crossing processes that make them a popular choice. However, the ultrafast internal conversion processes that precede the intersystem crossing are less frequently discussed in the literature. This work provides a comprehensive theoretical investigation of these nonadiabatic relaxation events in <i>meta</i>-methylbenzophenone utilizing spectroscopy techniques. Based on a full quantum mechanical description of the nonadiabatic dynamics, we simulate both time-dependent X-ray absorption and off-resonant-stimulated X-ray Raman spectra at the oxygen K-edge. We show that the use of time-resolved X-ray spectroscopy allows for a selective probing of the first singlet excited state by filtering out signals from other excited states with different electronic character. The element sensitivity of oxygen core level spectroscopy restricts the sensitivity to nonadiabatic processes localized at the carbonyl double bond.