Monitoring molecular nonadiabatic dynamics with femtosecond X-ray diffraction

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 115; no. 26; pp. 6538 - 6547
• Main Authors: Bennett, Kochise, Kowalewski, Markus, Rouxel, Jérémy R., Mukamel, Shaul
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 26.06.2018; Proceedings of the National Academy of Sciences
• Series: Inaugural Article
• Subjects: Charge density; Crystals; Density; Diffraction; Dynamical systems; Electronics; INAUGURAL ARTICLE; INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; Molecular biology; Photochemistry; Physical Sciences; Populations; Scaling; Time dependence; Variation; X-ray diffraction; X-ray scattering; x-ray diffraction; nonadiabatic dynamics; photochemistry; ultrafast dynamics
• ISSN: 0027-8424; 1091-6490; 1091-6490
• DOI: 10.1073/pnas.1805335115

Ultrafast time-resolved X-ray scattering, made possible by free-electron laser sources, provides a wealth of information about electronic and nuclear dynamical processes in molecules. The technique provides stroboscopic snapshots of the time-dependent electronic charge density traditionally used in structure determination and reflects the interplay of elastic and inelastic processes, nonadiabatic dynamics, and electronic populations and coherences. The various contributions to ultrafast off-resonant diffraction from populations and coherences of molecules in crystals, in the gas phase, or from single molecules are surveyed for core-resonant and off-resonant diffraction. Single-molecule α N scaling and two-molecule α N² scaling contributions, where N is the number of active molecules, are compared. Simulations are presented for the excited-state nonadiabatic dynamics of the electron harpooning at the avoided crossing in NaF. We show how a class of multiple diffraction signals from a single molecule can reveal charge-density fluctuations through multidimensional correlation functions of the charge density.