Nonlinear spectral dispersion in resonant Auger scattering from SF6 for studying nuclear potentials and dynamics

Abstract

In this study, we integrate experimental observations and theoretical models to elucidate the complex phenomena observed in the resonant S 𝐾-edge KLL Auger scattering spectra of the SF6 molecule. A two-dimensional spectral map, constructed of incident photon energy and kinetic energy of the emitted Auger electron, is shown to be a versatile tool for understanding a character of the core-excited potential energy surface and change of the molecular geometry. Our findings reveal how the distinct dispersion behavior of multiple spectral lines enables mapping of ultrafast dynamics within the short-lived core-excited states. Our results confirm the presence of nuclear dynamics in the S⁢1⁢𝑠−1⁢6⁢𝑎1 1⁢𝑔 and S⁢1⁢𝑠−1⁢6⁢𝑡1 1⁢𝑢 core-excited states, while dynamics is absent in the S⁢1⁢𝑠−1⁢7⁢𝑡1 1⁢𝑢 state. Using a combination of ab initio analysis, simulations with Coulomb model potentials, and a simple analytical approximation, we qualitatively demonstrate how the varying characteristics of spectral dispersion—classified as Raman, non-Raman, and anti-Raman—mirror the relative gradients of the intermediate and final states in the resonant x-ray scattering process. This insight allows for the effective mapping of molecular potential energy curves, offering a prospective tool on the underlying mechanisms of resonant Auger scattering and its potential for probing molecular dynamics.