Abstract
Quenching of vibrational excitations in resonant inelastic X-ray scattering (RIXS) spectra of liquid acetic acid is observed. At the oxygen core resonance associated with localized excitations at the O–H bond, the spectra lack the typical progression of vibrational excitations observed in RIXS spectra of comparable systems. We interpret this phenomenon as due to strong rehybridization of the unoccupied molecular orbitals as a result of hydrogen bonding, which however cannot be observed in x-ray absorption but only by means of RIXS. This allows us to address the molecular structure of the liquid, and to determine a lower limit for the average molecular chain length.
Highlights
Quenching of vibrational excitations in resonant inelastic X-ray scattering (RIXS) spectra of liquid acetic acid is observed
We show that the hydrogen bond (HB) has a dramatic influence on the molecular dynamics
Whereas ultrafast dissociation and accompanying extended vibrational progression are expected in RIXS spectra excited at the O–H antibonding intermediate state of O 1s−1σ ∗ character for the free molecule, the corresponding dynamics is almost entirely quenched in liquid acetic acid (ACA)
Summary
Quenching of vibrational excitations in resonant inelastic X-ray scattering (RIXS) spectra of liquid acetic acid is observed. At the oxygen core resonance associated with localized excitations at the O–H bond, the spectra lack the typical progression of vibrational excitations observed in RIXS spectra of comparable systems We interpret this phenomenon as due to strong rehybridization of the unoccupied molecular orbitals as a result of hydrogen bonding, which cannot be observed in x-ray absorption but only by means of RIXS. The dynamics is especially dramatic when the intermediate core-excited state is dissociative in a bond to a light atom, e.g., a state in which an O–H antibonding orbital is populated This dynamics is sensitively reflected in extended vibrational progressions in RIXS spectra, and the exploration of these phenomena for the investigation of HBs in the liquid phase is a new research field which we are currently entering. We will demonstrate that this by no means is a general rule
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