Probing hydrogen bond strength in liquid water by resonant inelastic X-ray scattering

Vinícius Vaz Da Cruz,Daniel Mcnally,Mattis Fondell,Raphael M Jay,Johannes Niskanen,Rafael C Couto,Michael Odelius,Xingye Lu,Annette Pietzsch,Faris Gel’Mukhanov,Sebastian Eckert,Alexander Föhlisch,Victor Kimberg,Marcus Dantz,Thorsten Schmitt,Marcella Iannuzzi,Emelie Ertan

doi:10.1038/s41467-019-08979-4

Abstract

Local probes of the electronic ground state are essential for understanding hydrogen bonding in aqueous environments. When tuned to the dissociative core-excited state at the O1s pre-edge of water, resonant inelastic X-ray scattering back to the electronic ground state exhibits a long vibrational progression due to ultrafast nuclear dynamics. We show how the coherent evolution of the OH bonds around the core-excited oxygen provides access to high vibrational levels in liquid water. The OH bonds stretch into the long-range part of the potential energy curve, which makes the X-ray probe more sensitive than infra-red spectroscopy to the local environment. We exploit this property to effectively probe hydrogen bond strength via the distribution of intramolecular OH potentials derived from measurements. In contrast, the dynamical splitting in the spectral feature of the lowest valence-excited state arises from the short-range part of the OH potential curve and is rather insensitive to hydrogen bonding.

Highlights

Local probes of the electronic ground state are essential for understanding hydrogen bonding in aqueous environments
Our simulations show that this shortening arises from variations in the OH potential energy curves (PECs), reflecting the different local hydrogen bond (HB) environments (Fig. 1c) in liquid water
We present a comprehensive ab initio analysis of the vibrational RIXS spectrum of water and show that the observed progression arises from coherent excitation of both OH bonds of a water molecule embedded in different local environments during the scattering process

Summary

Introduction

Local probes of the electronic ground state are essential for understanding hydrogen bonding in aqueous environments. The OH bonds stretch into the long-range part of the potential energy curve, which makes the X-ray probe more sensitive than infra-red spectroscopy to the local environment. We exploit this property to effectively probe hydrogen bond strength via the distribution of intramolecular OH potentials derived from measurements. Time-resolved pump-probe and multi-dimensional correlation spectroscopy using short IR pulses[1,2,3] provide insights into the structural dynamics of the HB network and the dynamics of vibrational energy redistribution These methods have been used to derive information of correlation or dephasing time and life-times, which have clarified the influence of hydrogen bonding on the IR spectrum. A molecular mechanism for the splitting was not explicitly given, the role of nuclear dynamics has been established by experimental observations[7] of an isotope effect of this transition (see refs. 8,9,11)

Methods

Results

Conclusion