Time-dependent quantum description of molecular double-core-hole-state formation: Impact of the nuclear dynamics on sequential two-photon processes

Abstract

We present a theoretical model to investigate double core hole states formation in molecules through sequential absorption of two x-ray photons from a femtosecond laser pulse. A complete time-dependent quantum description taking into account x-ray absorption and nuclear dynamics explicitly and Auger decay phenomenologically is established within the local approximation. Using this model, we assess the impact of the nuclear dynamics on double core photoionization processes in the case of the carbon monoxide molecule. We show that sequential absorption of two x-ray photons modifies significantly the vibrational distribution of the photoelectron spectra of the double core hole states compared to direct single x-ray photon absorption. Depending on the shape of the potential energy curves involved in the sequential absorption processes, lower or higher vibrational levels may be favoured. Furthermore, in case the final state is dissociative, the electron spectrum is further broaden and blue-shifted in the two-photon process.

The O K−2V spectrum of CO: the influence of the second core-hole

“…This is not the case in the present work, as the equivalent bond length of the molecule in its electronic ground state is at 1.128 Å, 69 while the bond length of the O doubly core-ionized CO has been calculated at 1.160 Å. 70 However, further investigations on similar systems like N 2 , NO, and O 2 are necessary to shed more light on the matter. Finally, multi-shake-up excitations involving the occupied MOs of the CO molecule have been observed and give rise to an intense above-threshold spectral feature.…”

Electron and fluorescence spectra of a water molecule irradiated by an x-ray free-electron laser pulse

“…The strong chemical sensitivity of double core-hole states [20][21][22][23][24][25][26][27][28][29][30][31][32] 2]. This demonstrates that at these high charge states the rearrangement of the hydrogen electrons towards the oxygen atom is completed.…”

“…[31]. Moreover, since we explore the whole parameter space by varying pulse durations and scanning through fluences, the computation of the electronic structure and the transition rates for all occurring molecular geometries would cause a tremendous computational effort.…”

“…These double core-hole states have received significant attention, because in electron spectroscopy they show more sensitivity to the chemical environment than single core-holes [21][22][23][24][25][26][27][28][29][30][31][32]. Moreover, the appearance of multiple core vacancies may help to reduce the radiation damage in prospective single-molecule coherent diffractive imaging experiments because they temporarily reduce the x-ray absorption in the sample [2,33].…”

Theoretical simulation of K−2V inner-shell processes in Ne and Ar

“…The outgoing wave would be mostly a p wave, and the symmetry of the K −2 V final state would be imposed by dipolar rules, therefore the same than that observed in conjugate lines for one photon K −2 V events. Moreover the associated cross sections could benefit from high photon fluxes On the theoretical side, the description of K −2 V processes by X-ray two-photon one color sequential ionization and excitation events is challenging because a competition between multiple x-ray photon absorption with nuclear dynamics and electronic Auger decay occurring at similar timescales is at play [6].…”