Ground state potential energy surfaces around selected atoms from resonant inelastic x-ray scattering.

Brian Kennedy,Conny Såthe,Jan-Erik Rubensson,Franz Hennies,Thorsten Schmitt,Simon Schreck,Piter S. Miedema,Annette Pietzsch,Alexander Föhlisch,Vladimir N. Strocov,Simone Techert

doi:10.1038/srep20054

Abstract

Thermally driven chemistry as well as materials’ functionality are determined by the potential energy surface of a systems electronic ground state. This makes the potential energy surface a central and powerful concept in physics, chemistry and materials science. However, direct experimental access to the potential energy surface locally around atomic centers and to its long-range structure are lacking. Here we demonstrate how sub-natural linewidth resonant inelastic soft x-ray scattering at vibrational resolution is utilized to determine ground state potential energy surfaces locally and detect long-range changes of the potentials that are driven by local modifications. We show how the general concept is applicable not only to small isolated molecules such as O2 but also to strongly interacting systems such as the hydrogen bond network in liquid water. The weak perturbation to the potential energy surface through hydrogen bonding is observed as a trend towards softening of the ground state potential around the coordinating atom. The instrumental developments in high resolution resonant inelastic soft x-ray scattering are currently accelerating and will enable broad application of the presented approach. With this multidimensional potential energy surfaces that characterize collective phenomena such as (bio)molecular function or high-temperature superconductivity will become accessible in near future.

Highlights

Final state experiences no broadening from the femtosecond lifetime of the core-excited intermediate state and no final state lifetime broadening since the final state is the electronic ground state
Using an incident bandwidth narrower than the intermediate state lifetime broadening, RIXS is uniquely suited to pick up low energy vibrational progressions with the elemental and chemical selectivity of the atomic soft x-ray scattering resonance[16,17,19,20,21,22,23]
Extrapolation of the potentials to internuclear distances and potential energies beyond the point where the vibrational progression is observed in the spectra is directly possible with an accuracy that is solely determined by the signal-to-noise ratio and spectral resolution of the experimental data

Summary

Liquid water

Final state experiences no broadening from the femtosecond lifetime of the core-excited intermediate state and no final state lifetime broadening since the final state is the electronic ground state. Our approach to the local ground state potential energy surface at the relevant sites and moieties within a large molecular aggregate or in condensed matter resembles finding a needle in a haystack The performance of this approach is conceptually open to even smaller energy scales and will benefit strongly from upcoming high-brilliance synchrotrons and free-electron lasers in combination with upcoming high resolution RIXS instruments. Multidimensional potential energy surfaces that characterize collective phenomena such as (bio)molecular function or high temperature superconductivity should become accessible with the ongoing instrumental developments in combination with ab initio derived potential energy surfaces

Methods and Materials

Author Contributions

Findings

Additional Information