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

Schäfer, Julia; Inhester, Ludger; Son, Sang−Kil; Fink, Reinhold F.; Santra, Robin

doi:10.1103/physreva.97.053415

Cited by 10 publications

(9 citation statements)

References 54 publications

(97 reference statements)

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“…1. In the low-fluence case (a), it is noticeable that the number of Auger decays decreases as the pulse duration becomes shorter, which is consistent with the observation in [34,44,45]. This is because Auger decays are beaten not only by M-shell photoabsorptions, but also by Nand O-shell photoabsorptions.…”

Section: A Pulse-duration Dependence Of Ionization Dynamicssupporting

confidence: 83%

Breakdown of frustrated absorption in x-ray sequential multiphoton ionization

Son

Boll

Santra

2020

Phys. Rev. Research

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We investigate the frustrated absorption phenomenon of atomic systems driven by x-ray pulses of extremely high intensity. When an atom is exposed to intense x-ray pulses generated by x-ray free-electron lasers (XFELs), it undergoes complex ionization dynamics characterized by sequential multiphoton multiple ionization. Counterintuitively, as the pulse duration becomes shorter so that the intensity increases, the ionization becomes suppressed because of hollow-atom formation and the reduction of cross section. This is called frustrated absorption. However, as we report here, the paradigm of frustrated absorption can break down at extremely high intensity. By using a state-of-the-art theoretical tool, we examine the pulse-duration dependence of x-ray multiphoton ionization dynamics of heavy atoms, revealing that the reduced ionization for shorter pulses is due to the suppression of Auger decays, rather than the frustration of photoabsorption. Moreover, we predict a situation where ionization is, in fact, enhanced as the pulse duration is decreased and explain the mechanism why this happens. The present results demonstrate that the breakdown of frustrated absorption will emerge at the highest fluence currently available at XFEL facilities and will play an important role when terawatt-attosecond x-ray pulses come into realization.

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Section: A Pulse-duration Dependence Of Ionization Dynamicssupporting

confidence: 83%

Breakdown of frustrated absorption in x-ray sequential multiphoton ionization

Son

Boll

Santra

2020

Phys. Rev. Research

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“…This dramatic enhancement of ionization can be explained by charge-rearrangement-enhanced x-ray ionization of molecules (CREXIM) [17]. Hard x-ray photons are absorbed almost exclusively by the iodine atom, because its cross section is much larger than that of the light atoms (σ I =0.052 Mb, σ C =7.5×10 −5 Mb, The CREXIM effect manifests itself not only in the produced charges, but also in electron and fluorescence spectra [34]. In our calculations, charge rearrangement is described via instantaneous orbital relaxation upon sequential ionization and molecular Auger decay [21].…”

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confidence: 99%

Theoretical evidence for the sensitivity of charge-rearrangement-enhanced x-ray ionization to molecular size

et al. 2019

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It was recently discovered that molecular ionization at high x-ray intensity is enhanced, in comparison with that of isolated atoms, through a phenomenon called CREXIM (charge-rearrangementenhanced x-ray ionization of molecules). X-ray absorption selectively ionizes heavy atoms within molecules, triggering electron transfer from neighboring atoms to the heavy atom sites and enabling further ionization there. The present theoretical study demonstrates that the CREXIM effect increases with the size of the molecule, as a consequence of increased intramolecular electron transfer from the larger molecular constituents attached to the heavy atoms. We compare x-ray multiphoton ionization dynamics of xenon, iodomethane, and iodobenzene after interacting with an intense x-ray pulse. Although their photoionization cross sections are similar, iodomethane and iodobenzene molecules are more ionized than xenon atoms. Moreover, we predict that the average total charge of iodobenzene is much larger than that of iodomethane, because of the large number of electrons in the benzene ring. The positive charges transferred from the iodine site to the benzene ring are redistributed such that the higher carbon charges are formed at the far end from the iodine site. Our first-principles calculations provide fundamental insights into the interaction of molecules with x-ray free-electron laser (XFEL) pulses. These insights need to be taken into account for interpreting and designing future XFEL experiments.X-ray free-electron lasers (XFELs) have opened new horizons for studying the structure and dynamics of matter with femtosecond temporal and atomic spatial resolution [1][2][3]. With the rapid advance in XFEL technology, the peak intensity already exceeds 10 20 W/cm 2 in the hard x-ray regime [4]. At extremely high x-ray intensity, it is crucial to understand the nonlinear interaction of atoms [5][6][7][8][9], molecules [10][11][12][13][14][15][16][17], and clusters [18-20] with xray fields. The interaction between matter and intense x-ray pulses can be described by the multiphoton multiple ionization dynamics model. An x-ray photon ionizes an atomic inner-shell electron, followed by relaxation processes. During the intense x-ray pulse the photoionization and accompanying processes repeat sequentially. This ionization model has been verified for atomic systems with a series of gas-phase XFEL experiments [5,7,8].When a molecule is irradiated by x rays, they mainly interact with heavy atoms within the molecule, because their photoionization cross section is much higher than that of light atoms. It had been widely believed that ionization dynamics of a molecule exposed to XFEL irradiation is similar to that of an isolated atom whose cross section is comparable to the molecule [12][13][14][15]. This expectation turned out to be valid in the low-fluence regime. For example, the total molecular ionization of methylselenol (CH 3 SeH) at low x-ray intensity, where single-photon absorption is dominant, was found to be similar to the atomic ionizat...

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“…Their unique properties have been used to study a diverse range of phenomena [7][8][9][10][11][12][13][14]. For many XFEL experiments a detailed, microscopic understanding of the radiation damage during the pulse exposure is crucial, e.g., to estimate the structural degradation in diffractive imaging experiments [8,15] or to interpret time-dependent spectroscopic signals [16,17]. However, the strong ionization by the x-ray pulses poses strong challenges for theoretical modeling.…”

Section: Introductionmentioning

confidence: 99%

“…To understand the interaction of intense x-ray light with matter, one must consider that a molecule interacting with the x-ray pulse may undergo a series of photoionization, fluorescence, and Auger decay processes eventually causing the ionization of a significant fraction of the electrons. It has been demonstrated that these ionization dynamics can be modeled via rate equations for the time-dependent populations of electronic configurations assuming multiple consecutive photoionization and electronic relaxation (Auger decay and fluorescence) steps [16,[18][19][20][21][22][23][24][25][26][27][28][29][30][31][32]. To that end the relevant cross sections and rates have to be provided.…”

Section: Introductionmentioning

confidence: 99%

“…To that end, we seek to calculate excited electronic states by employing a mean-field approximation directly solving the self-consistent-field (SCF) equation for excited electronic configurations [33][34][35][36][37][38][39][40][41][42]. In our previous works [16,25,28,31,43], we employed the excited state orbitals obtained with the Hartree-Fock-Slater (HFS) [44] method as implemented in the XMOLECULE toolkit [25,43] to obtain cross sections and rates. By solving the SCF equations for each electronic configuration, the molecular orbitals are adapted to the new electronic configuration after each photoionization, fluorescence, or Auger decay step.…”

Section: Introductionmentioning

confidence: 99%

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Strategies for solving the excited-state self-consistent-field problem for highly excited and multiply ionized states

2021

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The dynamics of molecules exposed to intense x-ray radiation involve a large number of multiply ionized and highly excited electronic configurations. To model these dynamics a reliable and efficient electronic structure model is imperative. Employing the Hartree-Fock-Slater electronic structure model in combination with the maximum overlap method, we quantify the associated convergence failures when calculating electronic states of carbon monoxide with multiple vacancies in the core and valence levels. We characterize these cases and describe strategies to overcome the convergence problems. The described techniques not only eliminate all convergence issues for CO but also result in a significant reduction of convergence failures for simulations of the x-rayinduced multiple ionization dynamics of the phenol molecule.

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

Cited by 10 publications

References 54 publications

Breakdown of frustrated absorption in x-ray sequential multiphoton ionization

Breakdown of frustrated absorption in x-ray sequential multiphoton ionization

Theoretical evidence for the sensitivity of charge-rearrangement-enhanced x-ray ionization to molecular size

Strategies for solving the excited-state self-consistent-field problem for highly excited and multiply ionized states

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