Coherent Vibrational Probes of Hydrogen Bond Structure Following Ultrafast Electron Transfer

摘要

We report measurements, ab initio calculations, and analytical models that reveal the coupling of low-frequency phonons to localized vibrations of a hydrogen-bonded organic crystal driven by ultrafast electron transfer. Fourier analysis of spectrally resolved oscillations in the transient reflectivity of mid-infrared probe pulses from single crystals of quinhydrone shows coupling between Raman-and IR-active intermolecular lattice phonons of this material. In addition, phonon coherence spectra of two of these lattice modes show that at least two qualitatively different vibrational transitions near 3000 cm(-1) exist in the charge-separated state of quinhydrone. This combined experimental and theoretical approach allows us to estimate the displacement of the O-H stretching vibration of quinhydrone along its different lattice phonon normal coordinates. These results will help better understand and approach a plethora of problems in condensed phases in which electronic and vibrational coupling over vastly different energy scales plays a significant role.