Molecular double core-hole electron spectroscopy for chemical analysis

TL;DR

This paper investigates double core hole electron spectroscopy as a tool for chemical analysis, proposing a method to extract relaxation energies and analyzing the influence of chemical environments on ionization potentials.

Contribution

It introduces a new approach to measure relaxation energies in double core-hole states using XTPPS and demonstrates its application on various small molecules.

Findings

Method to extract relaxation energies from ionization potentials.

Chemical environment affects double core-hole ionization potentials.

Relativistic effects on IPs and DIPs are briefly addressed.

Abstract

We explore the potential of double core hole electron spectroscopy for chemical analysis in terms of x-ray two-photon photoelectron spectroscopy (XTPPS). The creation of deep single and double core vacancies induces significant reorganization of valence electrons. The corresponding relaxation energies and the interatomic relaxation energies are evaluated by CASSCF calculations. We propose a method how to experimentally extract these quantities by the measurement of single and double core-hole ionization potentials (IPs and DIPs). The influence of the chemical environment on these DIPs is also discussed for states with two holes at the same atomic site and states with two holes at two different atomic sites. Electron density difference between the ground and double core-hole states clearly shows the relaxations accompanying the double core-hole ionization. The effect is also compared with the sensitivity of single core hole ionization potentials (IPs) arising in single core hole electron spectroscopy. We have demonstrated the method for a representative set of small molecules LiF, BeO, BF, CO, N2, C2H2, C2H4, C2H6, CO2 and N2O. The scalar relativistic effect on IPs and on DIPs are briefly addressed.