posted on 2024-01-26, 23:10authored bySambit K. Das, Marc-Oliver Winghart, Peng Han, Debkumar Rana, Zhuang-Yan Zhang, Sebastian Eckert, Mattis Fondell, Thomas Schnappinger, Erik T. J. Nibbering, Michael Odelius
Protons in low-barrier
superstrong hydrogen bonds are
typically
delocalized between two electronegative atoms. Conventional methods
to characterize such superstrong hydrogen bonds are vibrational spectroscopy
and diffraction techniques. We introduce soft X-ray spectroscopy to
uncover the electronic fingerprints for proton sharing in the protonated
imidazole dimer, a prototypical building block enabling effective
proton transport in biology and high-temperature fuel cells. Using
nitrogen core excitations as a sensitive probe for the protonation
status, we identify the X-ray signature of a shared proton in the
solvated imidazole dimer in a combined experimental and theoretical
approach. The degree of proton sharing is examined as a function of
structural variations that modify the shape of the low-barrier potential
in the superstrong hydrogen bond. We conclude by showing how the sensitivity
to the quantum distribution of proton motion in the double-well potential
is reflected in the spectral signature of the shared proton.