cometadata/datacite-titles-descriptions-related-identifiers huggingface dataset:
DOI: 10.6084/m9.figshare.1012486.v1
title: Cross sections at 91 eV photon energy and ionization potentials of N atoms and ions used in the simulation [29]

description: <b>Table 3.</b> Cross sections at 91 eV photon energy and ionization potentials of N atoms and ions used in the simulation [29]. <strong>Abstract</strong> Single-shot time-of-flight spectra for Coulomb explosion of N<sub>2</sub> and I<sub>2</sub> molecules have been recorded at the Free Electron LASer in Hamburg (FLASH) and have been analysed using a partial covariance mapping technique. The partial covariance analysis unravels a detailed picture of all significant Coulomb explosion pathways, extending up to the N<sup>4+</sup>–N<sup>5+</sup> channel for nitrogen and up to the I<sup>8+</sup>–I<sup>9+</sup> channel for iodine. The observation of the latter channel is unexpected if only sequential ionization processes from the ground state ions are considered. The maximum kinetic energy release extracted from the covariance maps for each dissociation channel shows that Coulomb explosion of nitrogen molecules proceeds much faster than that of the iodine. The N<sub>2</sub> ionization dynamics is modelled using classical trajectory simulations in good agreement with the outcome of the experiments. The results suggest that covariance mapping of the Coulomb explosion can be used to measure the intensity and pulse duration of free-electron lasers.
DOI: 10.6084/m9.figshare.1012484.v1
title: Maximum kinetic energy (KE) per fragment for N<sub>2</sub> extracted from figure 4(f) and from simulation; effective internuclear distances for all observed charge pairs

description: <b>Table 1.</b> Maximum kinetic energy (KE) per fragment for N<sub>2</sub> extracted from figure 4(f) and from simulation; effective internuclear distances for all observed charge pairs. Statistical uncertainties in the last digits are given in parentheses (two sigma); however, larger systematic errors may not be excluded. <strong>Abstract</strong> Single-shot time-of-flight spectra for Coulomb explosion of N<sub>2</sub> and I<sub>2</sub> molecules have been recorded at the Free Electron LASer in Hamburg (FLASH) and have been analysed using a partial covariance mapping technique. The partial covariance analysis unravels a detailed picture of all significant Coulomb explosion pathways, extending up to the N<sup>4+</sup>–N<sup>5+</sup> channel for nitrogen and up to the I<sup>8+</sup>–I<sup>9+</sup> channel for iodine. The observation of the latter channel is unexpected if only sequential ionization processes from the ground state ions are considered. The maximum kinetic energy release extracted from the covariance maps for each dissociation channel shows that Coulomb explosion of nitrogen molecules proceeds much faster than that of the iodine. The N<sub>2</sub> ionization dynamics is modelled using classical trajectory simulations in good agreement with the outcome of the experiments. The results suggest that covariance mapping of the Coulomb explosion can be used to measure the intensity and pulse duration of free-electron lasers.
DOI: 10.6084/m9.figshare.1012485.v1
title: Maximum kinetic energy (KE) per fragment for I<sub>2</sub> extracted from figure 5 and effective internuclear distances for all observed charge pairs

description: <b>Table 2.</b> Maximum kinetic energy (KE) per fragment for I<sub>2</sub> extracted from figure 5 and effective internuclear distances for all observed charge pairs. Statistical uncertainties in the last digits are given in parentheses (two sigma); however, larger systematic errors may not be excluded. <strong>Abstract</strong> Single-shot time-of-flight spectra for Coulomb explosion of N<sub>2</sub> and I<sub>2</sub> molecules have been recorded at the Free Electron LASer in Hamburg (FLASH) and have been analysed using a partial covariance mapping technique. The partial covariance analysis unravels a detailed picture of all significant Coulomb explosion pathways, extending up to the N<sup>4+</sup>–N<sup>5+</sup> channel for nitrogen and up to the I<sup>8+</sup>–I<sup>9+</sup> channel for iodine. The observation of the latter channel is unexpected if only sequential ionization processes from the ground state ions are considered. The maximum kinetic energy release extracted from the covariance maps for each dissociation channel shows that Coulomb explosion of nitrogen molecules proceeds much faster than that of the iodine. The N<sub>2</sub> ionization dynamics is modelled using classical trajectory simulations in good agreement with the outcome of the experiments. The results suggest that covariance mapping of the Coulomb explosion can be used to measure the intensity and pulse duration of free-electron lasers.
DOI: 10.6084/m9.figshare.1012464
title: Single-photon cross sections σ<sub><em>jk</em></sub> in units of 10<sup>−18</sup> cm<sup>2</sup>, from experiment [26, 30] (bold), using the GIPPER codeprotecthyperlink{jpb462020fn1}{$^{6}$} [31] (italic) and a fitting procedure [32]

description: <b>Table 1.</b> Single-photon cross sections σ<sub><em>jk</em></sub> in units of 10<sup>−18</sup> cm<sup>2</sup>, from experiment [26, 30] (bold), using the GIPPER code\protect\hyperlink{jpb462020fn1}{$^{6}$} [31] (italic) and a fitting procedure [32]. <strong>Abstract</strong> At the free-electron laser FLASH, multiple ionization of neon atoms was quantitatively investigated at photon energies of 93.0 and 90.5 eV. For ion charge states up to 6+, we compare the respective absolute photoionization yields with results from a minimal model and an elaborate description including standard sequential and direct photoionization channels. Both approaches are based on rate equations and take into account a Gaussian spatial intensity distribution of the laser beam. From the comparison we conclude that photoionization up to a charge of 5+ can be described by the minimal model which we interpret as sequential photoionization assisted by electron shake-up processes. For higher charges, the experimental ionization yields systematically exceed the elaborate rate-based prediction.
DOI: 10.6084/m9.figshare.1012464.v1
title: Single-photon cross sections σ<sub><em>jk</em></sub> in units of 10<sup>−18</sup> cm<sup>2</sup>, from experiment [26, 30] (bold), using the GIPPER codeprotecthyperlink{jpb462020fn1}{$^{6}$} [31] (italic) and a fitting procedure [32]

description: <b>Table 1.</b> Single-photon cross sections σ<sub><em>jk</em></sub> in units of 10<sup>−18</sup> cm<sup>2</sup>, from experiment [26, 30] (bold), using the GIPPER code\protect\hyperlink{jpb462020fn1}{$^{6}$} [31] (italic) and a fitting procedure [32]. <strong>Abstract</strong> At the free-electron laser FLASH, multiple ionization of neon atoms was quantitatively investigated at photon energies of 93.0 and 90.5 eV. For ion charge states up to 6+, we compare the respective absolute photoionization yields with results from a minimal model and an elaborate description including standard sequential and direct photoionization channels. Both approaches are based on rate equations and take into account a Gaussian spatial intensity distribution of the laser beam. From the comparison we conclude that photoionization up to a charge of 5+ can be described by the minimal model which we interpret as sequential photoionization assisted by electron shake-up processes. For higher charges, the experimental ionization yields systematically exceed the elaborate rate-based prediction.
DOI: 10.6084/m9.figshare.1012448
title: The electron energy and anisotropy parameters β<sub>2</sub> measured and calculated for the first-step photoelectrons from Xe in sequential 2PDI

description: <b>Table 1.</b> The electron energy and anisotropy parameters β<sub>2</sub> measured and calculated for the first-step photoelectrons from Xe in sequential 2PDI. The value labelled by * was fitted for energy calibration. <strong>Abstract</strong> Xenon atoms are double-ionized by sequential two-photon absorption by ultrashort extreme ultraviolet free-electron laser pulses with a photon energy of 23.0 and 24.3 eV, produced by the SPring-8 Compact SASE Source test accelerator. The angular distributions of photoelectrons generated by two-photon double ionization are obtained using velocity map imaging. The results are reproduced reasonably well by the present theoretical calculations within the multi-configurational Dirac–Fock approach.
DOI: 10.6084/m9.figshare.1012449
title: The electron energy and anisotropy parameters β<sub>2</sub> and β<sub>4</sub> measured and calculated for the second-step photoelectrons from Xe in sequential 2PDI

description: <b>Table 2.</b> The electron energy and anisotropy parameters β<sub>2</sub> and β<sub>4</sub> measured and calculated for the second-step photoelectrons from Xe in sequential 2PDI. <strong>Abstract</strong> Xenon atoms are double-ionized by sequential two-photon absorption by ultrashort extreme ultraviolet free-electron laser pulses with a photon energy of 23.0 and 24.3 eV, produced by the SPring-8 Compact SASE Source test accelerator. The angular distributions of photoelectrons generated by two-photon double ionization are obtained using velocity map imaging. The results are reproduced reasonably well by the present theoretical calculations within the multi-configurational Dirac–Fock approach.
DOI: 10.6084/m9.figshare.1012448.v1
title: The electron energy and anisotropy parameters β<sub>2</sub> measured and calculated for the first-step photoelectrons from Xe in sequential 2PDI

description: <b>Table 1.</b> The electron energy and anisotropy parameters β<sub>2</sub> measured and calculated for the first-step photoelectrons from Xe in sequential 2PDI. The value labelled by * was fitted for energy calibration. <strong>Abstract</strong> Xenon atoms are double-ionized by sequential two-photon absorption by ultrashort extreme ultraviolet free-electron laser pulses with a photon energy of 23.0 and 24.3 eV, produced by the SPring-8 Compact SASE Source test accelerator. The angular distributions of photoelectrons generated by two-photon double ionization are obtained using velocity map imaging. The results are reproduced reasonably well by the present theoretical calculations within the multi-configurational Dirac–Fock approach.
DOI: 10.6084/m9.figshare.1012449.v1
title: The electron energy and anisotropy parameters β<sub>2</sub> and β<sub>4</sub> measured and calculated for the second-step photoelectrons from Xe in sequential 2PDI

description: <b>Table 2.</b> The electron energy and anisotropy parameters β<sub>2</sub> and β<sub>4</sub> measured and calculated for the second-step photoelectrons from Xe in sequential 2PDI. <strong>Abstract</strong> Xenon atoms are double-ionized by sequential two-photon absorption by ultrashort extreme ultraviolet free-electron laser pulses with a photon energy of 23.0 and 24.3 eV, produced by the SPring-8 Compact SASE Source test accelerator. The angular distributions of photoelectrons generated by two-photon double ionization are obtained using velocity map imaging. The results are reproduced reasonably well by the present theoretical calculations within the multi-configurational Dirac–Fock approach.
DOI: 10.6084/m9.figshare.1012428
title: Experimentally obtained anisotropy parameters β<sub>2</sub> and β<sub>4</sub>, and the extracted values of <em>W</em> and Δ

description: <b>Table 1.</b> Experimentally obtained anisotropy parameters β<sub>2</sub> and β<sub>4</sub>, and the extracted values of <em>W</em> and Δ. <strong>Abstract</strong> The two-photon ionization of helium atoms by ultrashort extreme-ultraviolet free-electron laser pulses, produced by the SPring-8 Compact SASE Source test accelerator, was investigated at photon energies of 20.3, 21.3, 23.0 and 24.3 eV. The angular distribution of photoelectrons generated by two-photon ionization is obtained using a velocity map imaging spectrometer. The phase-shift differences and amplitude ratios of the outgoing s and d continuum wave packets are extracted from the photoelectron angular distributions. The obtained values of the phase-shift differences are distinct from scattering phase-shift differences when the photon energy is tuned to a resonance with an excited level or Rydberg manifold. The difference stems from the co-presence of resonant and non-resonant path contributions in the two-photon ionization by femtosecond pulses. Since the relative contribution of both paths can be controlled in principle by the pulse shape, these results illustrate a new way to tailor the continuum wave packet.
DOI: 10.6084/m9.figshare.1012424
title: Transition dipole moments (atomic units) from the core hole to the final states of CO<sup>+</sup> (figure 1) at the equilibrium geometry computed on the MCSCF level with the cc-pvtz basis set using the MOLPRO <em>ab initio</em> package [18]

description: <b>Table 1.</b> Transition dipole moments (atomic units) from the core hole to the final states of CO<sup>+</sup> (figure 1) at the equilibrium geometry computed on the MCSCF level with the cc-pvtz basis set using the MOLPRO <em>ab initio</em> package [18]. <strong>Abstract</strong> We theoretically demonstrate the feasibility of x-ray lasing in the CO molecule by the core ionization of the C K- and O K-shell by x-ray free-electron laser sources. Our numerical simulations are based on the solution of generalized Maxwell–Bloch equations, accounting for the electronic and nuclear degrees of freedom. The amplified x-ray emission pulses have an extremely narrow linewidth of about 0.1 eV and a pulse duration shorter than 30 fs. We compare x-ray lasing transitions to the three lowest electronic states of singly ionized CO. The dependence of the lasing efficiency on the spectral width of the x-ray fluorescence band, value and orientation of the electronic transition dipole moment, lifetime of the core-excited state and the duration of the pump pulse is analysed. Using a pre-aligned molecular ensemble substantially increases the amplified emission. Moreover, by controlling the molecular alignment and thereby the alignment of the transition dipole moment polarization, the control of the emitted x-ray radiation is achievable. Preparing the initial vibrational quantum state, the x-ray emission frequency can be tuned within the fluorescence band. The present scheme is applicable to other diatomic systems, thereby extending the spectral range of coherent x-ray radiation sources based on stimulated x-ray emission on bound transitions.
DOI: 10.6084/m9.figshare.1012424.v1
title: Transition dipole moments (atomic units) from the core hole to the final states of CO<sup>+</sup> (figure 1) at the equilibrium geometry computed on the MCSCF level with the cc-pvtz basis set using the MOLPRO <em>ab initio</em> package [18]

description: <b>Table 1.</b> Transition dipole moments (atomic units) from the core hole to the final states of CO<sup>+</sup> (figure 1) at the equilibrium geometry computed on the MCSCF level with the cc-pvtz basis set using the MOLPRO <em>ab initio</em> package [18]. <strong>Abstract</strong> We theoretically demonstrate the feasibility of x-ray lasing in the CO molecule by the core ionization of the C K- and O K-shell by x-ray free-electron laser sources. Our numerical simulations are based on the solution of generalized Maxwell–Bloch equations, accounting for the electronic and nuclear degrees of freedom. The amplified x-ray emission pulses have an extremely narrow linewidth of about 0.1 eV and a pulse duration shorter than 30 fs. We compare x-ray lasing transitions to the three lowest electronic states of singly ionized CO. The dependence of the lasing efficiency on the spectral width of the x-ray fluorescence band, value and orientation of the electronic transition dipole moment, lifetime of the core-excited state and the duration of the pump pulse is analysed. Using a pre-aligned molecular ensemble substantially increases the amplified emission. Moreover, by controlling the molecular alignment and thereby the alignment of the transition dipole moment polarization, the control of the emitted x-ray radiation is achievable. Preparing the initial vibrational quantum state, the x-ray emission frequency can be tuned within the fluorescence band. The present scheme is applicable to other diatomic systems, thereby extending the spectral range of coherent x-ray radiation sources based on stimulated x-ray emission on bound transitions.
DOI: 10.6084/m9.figshare.1012396
title: Core-level tsDIP, SIP, IR energy, modified second IP (IP*) (in eV) and polarizability (α) calculated by the <em>ab initio</em> SCF method with the cc-pCVTZ basis set

description: <b>Table 1.</b> Core-level tsDIP, SIP, IR energy, modified second IP (IP*) (in eV) and polarizability (α) calculated by the <em>ab initio</em> SCF method with the cc-pCVTZ basis set. <strong>Abstract</strong> The interatomic relaxation (IR) effects of two-site double core hole (tsDCH) states in selected molecules with a polarizable unit have been systematically investigated using <em>ab initio</em> calculations. The IR effects are analysed by varying the size of this polarizable unit and its position relative to the DCHs. The systems with the DCHs located on the opposite sides of the polarizable unit show large negative IR energies, while those on the same side of the polarizable unit have smaller negative IR effects. Here, the IR energies can even be positive if the polarizable unit is large enough. The generalized Wagner plots of tsDCH states are used to visualize the trend of the IR effects in the molecules studied.
DOI: 10.6084/m9.figshare.1012396.v1
title: Core-level tsDIP, SIP, IR energy, modified second IP (IP*) (in eV) and polarizability (α) calculated by the <em>ab initio</em> SCF method with the cc-pCVTZ basis set

description: <b>Table 1.</b> Core-level tsDIP, SIP, IR energy, modified second IP (IP*) (in eV) and polarizability (α) calculated by the <em>ab initio</em> SCF method with the cc-pCVTZ basis set. <strong>Abstract</strong> The interatomic relaxation (IR) effects of two-site double core hole (tsDCH) states in selected molecules with a polarizable unit have been systematically investigated using <em>ab initio</em> calculations. The IR effects are analysed by varying the size of this polarizable unit and its position relative to the DCHs. The systems with the DCHs located on the opposite sides of the polarizable unit show large negative IR energies, while those on the same side of the polarizable unit have smaller negative IR effects. Here, the IR energies can even be positive if the polarizable unit is large enough. The generalized Wagner plots of tsDCH states are used to visualize the trend of the IR effects in the molecules studied.
DOI: 10.6084/m9.figshare.1012387
title: PSDs, bandwidths and coherence times, for fields with exponential and Gaussian correlations

description: <b>Table 1.</b> PSDs, bandwidths and coherence times, for fields with exponential and Gaussian correlations. <strong>Abstract</strong> Motivated by recent experiments pertaining to the interaction of weak SASE-free-electron-laser (FEL) pulses with atoms and molecules, we investigate the conditions under which such interactions can be described in the framework of a simple phase-diffusion model with decorrelated atom–field dynamics. The nature of the fluctuations that are inevitably present in SASE-FEL pulses is shown to play a pivotal role in the success of the decorrelation. Our analysis is performed in connection with specific recent experimental results from FLASH in the soft x-ray regime.
DOI: 10.6084/m9.figshare.1012387.v1
title: PSDs, bandwidths and coherence times, for fields with exponential and Gaussian correlations

description: <b>Table 1.</b> PSDs, bandwidths and coherence times, for fields with exponential and Gaussian correlations. <strong>Abstract</strong> Motivated by recent experiments pertaining to the interaction of weak SASE-free-electron-laser (FEL) pulses with atoms and molecules, we investigate the conditions under which such interactions can be described in the framework of a simple phase-diffusion model with decorrelated atom–field dynamics. The nature of the fluctuations that are inevitably present in SASE-FEL pulses is shown to play a pivotal role in the success of the decorrelation. Our analysis is performed in connection with specific recent experimental results from FLASH in the soft x-ray regime.
DOI: 10.6084/m9.figshare.1012377
title: Parameters for PI and RA decay of CO* utilized in the present calculations

description: <b>Table 1.</b> Parameters for PI and RA decay of CO* utilized in the present calculations. The energy of the exciting radiation is chosen to be ω = 534.2 eV. <strong>Abstract</strong> The dynamics of the resonant Auger (RA) decay of the core-excited CO*(1s<sup>−1</sup>π*) molecule in intense x-ray laser pulses is studied theoretically. The present approach includes the impact of the analogue of conical intersections of the complex potential energy surfaces of the ground and 'dressed' resonant states induced by intense x-ray pulses. It also takes into account the decay of the resonance and the direct photoionization of the ground state, both populating the same final ionic states coherently, as well as the direct photoionization of the resonance state itself. The individual impacts of these physical processes on the total ion yield, the CO<sup>+</sup>(<em>A</em> <sup>2</sup>Π) electron spectrum and the ro-vibrational distributions of the neutral molecules remaining in the ground electronic state after the laser pulse has expired are analysed and compared to those reported previously for the C*O resonance. It is also demonstrated that the RA effect of molecules by strong laser pulses of resonant carrier frequency is an efficient process to produce <em>two-site double-core-hole–one-particle</em> states of CO*.
DOI: 10.6084/m9.figshare.1012377.v1
title: Parameters for PI and RA decay of CO* utilized in the present calculations

description: <b>Table 1.</b> Parameters for PI and RA decay of CO* utilized in the present calculations. The energy of the exciting radiation is chosen to be ω = 534.2 eV. <strong>Abstract</strong> The dynamics of the resonant Auger (RA) decay of the core-excited CO*(1s<sup>−1</sup>π*) molecule in intense x-ray laser pulses is studied theoretically. The present approach includes the impact of the analogue of conical intersections of the complex potential energy surfaces of the ground and 'dressed' resonant states induced by intense x-ray pulses. It also takes into account the decay of the resonance and the direct photoionization of the ground state, both populating the same final ionic states coherently, as well as the direct photoionization of the resonance state itself. The individual impacts of these physical processes on the total ion yield, the CO<sup>+</sup>(<em>A</em> <sup>2</sup>Π) electron spectrum and the ro-vibrational distributions of the neutral molecules remaining in the ground electronic state after the laser pulse has expired are analysed and compared to those reported previously for the C*O resonance. It is also demonstrated that the RA effect of molecules by strong laser pulses of resonant carrier frequency is an efficient process to produce <em>two-site double-core-hole–one-particle</em> states of CO*.