Resonant Double-Core Excitations with Ultrafast, Intense Pulses

TL;DR

This paper explores the use of ultrafast, intense soft x-ray pulses to induce and analyze double-core-hole states in molecules, revealing site-specific excitation mechanisms and decay pathways through advanced simulations.

Contribution

It introduces a theoretical framework combining multiconfigurational calculations and TDSE simulations to study resonant double-core excitations and their decay in N2O molecules.

Findings

Reduced second core-excitation energy compared to ground state

Site-selective double core-excitation mechanism demonstrated

Predicted changes in electron emission lineshapes with photon absorption

Abstract

Intense few-to-sub-femtosecond soft x-ray pulses can produce neutral, two-site excited double-core-hole states by promoting two core electrons to the same unoccupied molecular orbital. We theoretically investigate double nitrogen K-edge excitations of nitrous oxide (N2O) with multiconfigurational electronic structure calculations. We show that the second core-excitation energy is reduced with respect to its ground state value. A site-selective double core-excitation mechanism using intense few-femtosecond x-rays is investigated using time-dependent Schrodinger equation (TDSE) simulations. The subsequent two-step Auger-Meitner and two-electrons-one-electron decay spectra of the double core-excited states are analyzed using a Mulliken population analysis of the multiconfirational wavefunctions. The change in the electron emission lineshape between the absorption of 1 or 2 photons in the resonant core-excitation is predicted by combining this approach with the TDSE simulations. We examine the possibility of resolving the double core-excited states with x-ray pump-probe techniques by calculating the chemical shifts of the core-electron binding energy of the core-excited states and decay products.