Formation and relaxation of K−2 and K−2V double-core-hole states in n-butane

Abstract

Using a magnetic bottle multi-electron time-of-flight spectrometer in combination with synchrotron radiation, double-core-hole pre-edge and continuum states involving the K-shell of the carbon atoms in n-butane ( n-C4H10) have been identified, where the ejected core electron(s) and the emitted Auger electrons from the decay of such states have been detected in coincidence. An assignment of the main observed spectral features is based on the results of multi-configurational self-consistent field (MCSCF) calculations for the excitation energies and static exchange (STEX) calculations for energies and intensities. MCSCF results have been analyzed in terms of static and dynamic electron relaxation as well as electron correlation contributions to double-core-hole state ionization potentials. The analysis of applicability of the STEX method, which implements the one-particle picture toward the complete basis set limit, is motivated by the fact that it scales well toward large species. We find that combining the MCSCF and STEX techniques is a viable approach to analyze double-core-hole spectra.

Core-Excited States and X-ray Absorption Spectra from Multireference Algebraic Diagrammatic Construction Theory

“…While this assumption is valid for many closed-shell molecules at (or near) equilibrium geometries, XAS is increasingly being used to probe core-level excited states of chemical systems with more challenging electronic structures, such as radicals, − transition-metal complexes, − and along the dissociative reaction pathways − where multireference effects can be significant. However, in contrast to single-reference theories, the range of available multireference methods is much narrower, including implementations of multiconfigurational self-consistent field, − multireference perturbation theories, − configuration interaction, − coupled cluster, ,− and driven similarity renormalization group approaches. − …”