Resolving vibrations in a polyatomic molecule with femtometer precision via x-ray spectroscopy

Abstract

We measure molecular vibrations with femtometer precision via resonance energy shifts using time-resolved x-ray absorption spectroscopy. For a demonstration, a Raman process excites the ${A}_{1g}$ mode in gas-phase ${\mathrm{SF}}_{6}$ molecules with an amplitude of approximately $50\phantom{\rule{4pt}{0ex}}\mathrm{fm}$, which is probed by a time-delayed soft-x-ray pulse at the sulfur ${L}_{2,3}$ edge. Mapping the extremely small measured energy shifts to internuclear distances requires an understanding of the electronic contributions provided by a many-body ab initio simulation. Our study establishes core-level spectroscopy as a precision tool for time-dependent molecular-structure metrology.