Capturing Coupled\nStructural and Electronic Motions\nDuring Excited-State Intramolecular Proton Transfer via Computational\nMultiedge Resonant Inelastic X‑ray Scattering

Proton transfer processes form the foundation of many\nchemical\nprocesses. In excited-state intramolecular proton transfer (ESIPT)\nprocesses, ultrafast proton transfer is impulsively initiated through\nlight. Here, we explore time-dependent coupled atomic and electronic\nmotions during and following ESIPT through computational time-resolved\nresonant inelastic X-ray scattering (RIXS). Excited-state ab initio\nmolecular dynamics simulations combined with time-dependent density\nfunctional theory calculations were performed for a model ESIPT system,\n10-hydroxybenzo[h]quinoline, to obtain transient RIXS signatures.\nThe RIXS spectra at both the nitrogen and oxygen K-edges were computed\nto resolve the electronic and atomic structural dynamics from both\nthe proton donor and acceptor perspective. The results demonstrate\nthat RIXS provides unprecedented details of the local electronic structure,\nthe coupling between different core and valence excited electronic\nstates, and the reorganization of the electronic structure coupled\nto the proton transfer process. We also develop a spectroscopic ruler\ncorrelating spectral shifts of a RIXS peak to the proton transfer\ndistance during ESIPT. This work highlights the exciting potential\nof time-resolved RIXS experiments at newly commissioned soft X-ray\nfree electron laser facilities for measuring coupled electronic and\nstructural changes during ultrafast chemical processes.