Femtosecond x-ray absorption spectroscopy of pyrazine at the nitrogen K-edge: on the validity of the Lorentzian limit. (22nd December 2021)

• Record Type: Journal Article
• Authors: Freibert, Antonia; Mendive-Tapia, David; Huse, Nils; Vendrell, Oriol
• Is Part Of: Journal of physics. Volume 54:Number 24(2021)
• Publication Date: 2021-12-22
• Subjects: transient x-ray absorption spectroscopy -- multiconfiguration time-dependent Hartree -- non-adiabatic molecular dynamics -- short-time approximation -- Lorentzian limit -- molecule-light interaction; Atoms -- Periodicals; Molecules -- Periodicals; Optics -- Periodicals; Nuclear physics -- Periodicals; 539.6
• DOI: 10.1088/1361-6455/ac3846
• Languages: English
• ISSNs: 0953-4075

Abstract

Abstract: We calculate the femtosecond x-ray absorption spectrum of pyrazine at the nitrogen K-edge including the wavepacket dynamics in both the valence and core-excited state manifolds. We do not invoke the widely used short-time (or Lorentzian) approximation which neglects the nuclear dynamics after the x-ray probe excitation. Instead, we calculate the x-ray-induced polarization in the time-domain where the optical pump as well as x-ray probe pulses are explicitly described. While the non-adiabatic population transfer following the optical excitation is well reproduced in the Lorentzian limit the transient x-ray absorption spectra obtained under this approximation lack some vibronic features, even when considering the short core-hole lifetime of nitrogen. We further demonstrate the effect of an increasingly longer pulse on the observed photo-triggered wavepacket dynamics which are blurred to the point that the x-ray probe response becomes effectively time-independent.