Unexpected dipole instabilities in small molecules after ultrafast XUV irradiation

Abstract

We investigate the depletion of deep-lying single-electron states in the N2 dimer under the influence of very short XUV pulses. We find, first, a marked occupation inversion for a certain window of XUV energies around 50 eV where depletion of the deepest bound valence electron state is much larger than for any other state, and second, that this occupation inversion drives a dipole instability, i.e. a spontaneous reappearance of the dipole signal long after the laser pulse is over and the initial dipole oscillations died out. As a tool for this study, we use time-dependent density functional theory with a self-interaction correction solved on a coordinate-space grid with absorbing boundary conditions. Key observables are state-specific electron emission (depletion) and photoelectron spectra (PES). The dipole instability generates additional electron emission leading to a specific low-energy structure in PES, a signal which could be used to identify the dipole instability experimentally. The here reported dedicated depletion of a deep lying electron state by a well tuned XUV pulse has been found also in other atoms and molecules. It provides a practicable realization of an instantaneously produced deep hole state, a situation which is often assumed ad hoc in numerous theoretical studies of energetic ultrafast processes. Moreover, the identification of the subsequent dipole instability by PES will allow one to study basic decay channels of hole states in detail.

Size Effect in Correlation-Driven Charge Migration in Correlation Bands of Alkyne Chains

“…In addition, it was shown to be a realistic situation for ionization with ultrashort laser pulses. 53 Our initial state is therefore created by removing an electron from one of the two orbitals at t = 0. The initial state is then propagated using the multielectron wave packet propagation method.…”

“…It is usually a very good approximation for high-energy photon ionization and was found to be a good approximation in the context of charge migration by Ayuso et al who performed simulations with and without it. In addition, it was shown to be a realistic situation for ionization with ultrashort laser pulses . Our initial state is therefore created by removing an electron from one of the two orbitals at t = 0.…”