JOSE LUIS SANZ VICARIO - Academia.edu (original) (raw)
Papers by JOSE LUIS SANZ VICARIO
Home Search Collections Journals About Contact us My IOPscience You may also be interested in: Ti... more Home Search Collections Journals About Contact us My IOPscience You may also be interested in: Time-resolved resonant photoionization of He using a time-dependent Feshbach method with ultrashort laser pulses C M Granados-Castro and J L Sanz-Vicario Time-resolved resonant photoionization of He using a time-dependent Feshbach method with ultrashort laser pulses C M Granados-Castro and J L Sanz-Vicario Reply to comment on 'Time-resolved resonant photoionization of He using a time-dependent Feshbach method with ultrashort laser pulses'
Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licenc... more Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.
ABSTRACT We study the resonant photoionization of the Helium atom subject to ultrashort laser pul... more ABSTRACT We study the resonant photoionization of the Helium atom subject to ultrashort laser pulses by using a Feshbach formalism in the time domain. We solve the projected time-dependent Schrodinger equation in terms of a configuration interaction spectral method, with a total wave function expanded with configurations defined within bound-like ( ##IMG## [http://ej.iop.org/images/1742-6596/488/3/032023/jpconf14_488_032023_eqn001.gif] ) and scattering-like ( ##IMG## [http://ej.iop.org/images/1742-6596/488/3/032023/jpconf14_488_032023_eqn002.gif] ) halfspaces. The method allows for accurate descriptions of both the atomic structure (energy positions and widths) as well as for the resonant photodynamics using ultrashort laser pulses. Special attention is given to the temporal formation of Fano profiles in the one- and two-photon ionization cross sections.
The presence of net circular dichroism in the photoionization of nonchiral homonuclear molecules ... more The presence of net circular dichroism in the photoionization of nonchiral homonuclear molecules has been put in evidence recently through the measurement of molecular-frame photoelectron angular distributions in dissociative photoionization of H 2 [Dowek et al., Phys. Rev. Lett. 104, 233003 (2010)]. In this work we present a detailed study of circular dichroism in the photoelectron angular distributions of H 2 and D 2 molecules, oriented perpendicularly to the propagation vector of the circularly polarized light, at different photon energies (20, 27, and 32.5 eV). Circular dichroism in the angular distributions at 20 and to a large extent 27 eV exhibits the usual pattern in which inversion symmetry is preserved. In contrast, at 32.5 eV, the inversion symmetry breaks down, which eventually leads to total circular dichroism after integration over the polar emission angle. Time-dependent ab initio calculations support and explain the observed results for H 2 in terms of quantum interferences between direct photoionization and delayed autoionization from the Q 1 and Q 2 doubly excited states into ionic states (1sσ g and 2pσ u) of different inversion symmetry. Nevertheless, for D 2 at 32.5 eV, there is a particular case where theory and experiment disagree in the magnitude of the symmetry breaking: when D + ions are produced with an energy of around 5 eV. This reflects the subleties associated to such simple molecules when exposed to this fine scrutiny.
Synopsis Shannon entropies and Fisher information calculated from one-particle density distributi... more Synopsis Shannon entropies and Fisher information calculated from one-particle density distributions and von Neumann and linear entropies (the latter two as a measure of entanglement) computed from the reduced oneparticle density matrix are analyzed for the 1,3 S e , 1,3 P o and 1,3 D e Rydberg series of He doubly excited states below the second ionization threshold. We find that both Fisher information and entanglement measures are able to discriminate resonances pertaining to different (K, T) A series.
Physical review letters, Jan 22, 2011
We report experiments where hydrogen molecules were dissociatively ionized by an attosecond pulse... more We report experiments where hydrogen molecules were dissociatively ionized by an attosecond pulse train in the presence of a near-infrared field. Fragment ion yields from distinguishable ionization channels oscillate with a period that is half the optical cycle of the IR field. For molecules aligned parallel to the laser polarization axis, the oscillations are reproduced in two-electron quantum simulations, and can be explained in terms of an interference between ionization pathways that involve different harmonic orders and a laser-induced coupling between the 1sσ(g) and 2pσ(u) states of the molecular ion. This leads to a situation where the ionization probability is sensitive to the instantaneous polarization of the molecule by the IR electric field and demonstrates that we have probed the IR-induced electron dynamics with attosecond pulses.
Physical Review a, 2003
We report calculated photodetachment cross sections from the metastable Be Ϫ 1s 2 2s2p 2 4 P e st... more We report calculated photodetachment cross sections from the metastable Be Ϫ 1s 2 2s2p 2 4 P e state in the photon energy range 0-10 eV. Outer-shell photodetachment takes place in this energy range, which includes the double-ionization threshold Be ϩ (2 S e) at ϳ7 eV as well as doubly excited thresholds of the residual atom up to the Be(1s 2 2p4 f) threshold at ϳ10 eV. Therefore, triply excited states of Be Ϫ are reached within the selected photon energy. We have implemented the complex scaled configuration interaction method along with a model potential for the 1s 2 core to uncover the first series of Be Ϫ 4 L o resonant states. In this work, four 4 P o , seven 4 D o , and two 4 S o resonances are reported and we compare our cross section with other previous theoretical calculations, that reported none or, at most, two resonances.
Physical Review Letters, 2010
Circular dichroism is a consequence of chirality. However, nonchiral molecules can also exhibit i... more Circular dichroism is a consequence of chirality. However, nonchiral molecules can also exhibit it when the measurement itself introduces chirality, e.g., when measuring molecular-frame photoelectron angular distributions. The few such experiments performed on homonuclear diatomic molecules show that, as expected, circular dichroism vanishes when the molecular-frame photoelectron angular distributions are integrated over the polar electron emission angle. Here we show that this is not the case in resonant dissociative ionization of H 2 for photons of 30-35 eV, which is the consequence of the delayed ionization from molecular doubly excited states into ionic states of different inversion symmetry.
Physical Review A, 2006
We present a nonperturbative time-dependent theoretical method to study H 2 ionization with femto... more We present a nonperturbative time-dependent theoretical method to study H 2 ionization with femtosecond laser pulses when the photon energy is large enough to populate the Q 1 ͑25-28 eV͒ and Q 2 ͑30-37 eV͒ doubly excited autoionizing states. We have investigated the role of these states in dissociative ionization of H 2 and analyzed, in the time domain, the onset of the resonant peaks appearing in the proton kinetic energy distribution. Their dependence on photon frequency and pulse duration is also analyzed. The results are compared with available experimental data and with previous theoretical results obtained within a stationary perturbative approach. The method allows us as well to obtain dissociation yields corresponding to the decay of doubly excited states into two H atoms. The calculated H͑n =2͒ yields are in good agreement with the experimental ones.
Physical Review A, 2010
Using a novel split-mirror setup attached to a Reaction Microscope at the Free electron LASer in ... more Using a novel split-mirror setup attached to a Reaction Microscope at the Free electron LASer in Hamburg (FLASH) we demonstrate an XUV-pump-XUV-probe
Physical Review A, 2009
Photoelectron angular distributions from fixed-in-space H 2 molecules exposed to ultrashort xuv l... more Photoelectron angular distributions from fixed-in-space H 2 molecules exposed to ultrashort xuv laser pulses have been evaluated. The theoretical method is based on the solution of the time-dependent Schrödinger equation in a basis of stationary states that include all electronic and vibrational degrees of freedom. Asymmetric angular distributions are observed as a consequence of the delayed ionization from the H 2 doubly excited states, which induces interferences between gerade and ungerade ionization channels. The analysis of this asymmetry as a function of pulse duration can provide an estimate of the corresponding autoionization widths.
Physical Review A, 2013
We have implemented a method based on the Feshbach formalism along with an explicitly correlated ... more We have implemented a method based on the Feshbach formalism along with an explicitly correlated configuration interaction method to perform a systematic study on the behavior of resonance parameters (energies and lifetimes) of the autoionizing states of plasma-embedded He 1,3 S e , 1,3 P o , and 1,3 D e , as a function of the screening strength. In particular, we study the evolution of the lowest states in the series located below the He + (N = 2) ionization threshold in the unscreened case. At variance with one-electron atoms (where shape resonance widths vary monotonically with the screening strength) the evolution of the Auger width with respect to screening is found to be different for each series represented by (K,T) A pseudoquantum numbers until resonances merge into the upper electronic continuum, when crossing the He + (2s) threshold. We conclude from our ab initio calculations that, although resonances pertaining to the same (K,T) A series share a similar tendency in their widths against the screening strength, general propensity rules for the robustness of lifetimes, based on the isomorphic series in the (K,T) A classification, cannot be established in plasma-embedded helium.
Physical Review A, 2002
The K-shell photodetachment of the metastable 1s2s2p 4 P o He - state is calculated ab initio wit... more The K-shell photodetachment of the metastable 1s2s2p 4 P o He - state is calculated ab initio with a complex scaled configuration interaction method in the photon energy region between the He 2s2p 3 P o threshold and the second double ionization threshold He + (n=2). ...
Physical Review A, 2002
The photodetachment of the metastable He Ϫ 1s2s2p 4 P o state has been calculated in two photon e... more The photodetachment of the metastable He Ϫ 1s2s2p 4 P o state has been calculated in two photon energy regions of interest: the first, named here as energy region I, below the double photoionization threshold He ϩ (nϭ1), involving outer-shell ionization and doubly excited states of He Ϫ , and the second, named here as region II, above the He Ϫ 1s ionization threshold and below the He ϩ (nϭ2) threshold, involving K-shell detachment and triply excited states of a He Ϫ ''hollow ion.'' We have implemented an ab initio three-electron configuration-interaction method in the LS-coupling scheme combined with complex scaling to obtain resonance positions and widths and the photodetachment cross sections. We have revisited region I, although widely studied before, as a test of our method. Notwithstanding some small discrepancies, our complex scaling results compare well with the previously published results and also add new understanding to some features in the cross section. Our emphasis is given to K-shell photodetachment in photon energy region II, where comparison is made with two other recent theoretical calculations that use completely different methods, and that were in dispute. We also compare with a very recent experiment for the He Ϫ K-shell photodetachment, which displays three major features; a broad nonresonant hump after the He 2s2p 3 P o threshold and two other peaks. A complex scaling analysis of prominent structures in the photodetachment spectra in region II, previously claimed to be nonresonant structures, leads to a different conclusion; i.e., they are all true triply excitedstate resonances, and two of them correspond to the peaks observed experimentally.
![Research paper thumbnail of Outer-shell photodetachment of the metastable Mg^{−} [core]3s3p^{2} and Ca^{−} [core]4s4p^{2} ^{4}P^{e} states](https://attachments.academia-assets.com/102793827/thumbnails/1.jpg)
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Physical Review A, 2008
We report on calculated outer-shell photodetachment cross sections from the metastable ͓core͔nsnp... more We report on calculated outer-shell photodetachment cross sections from the metastable ͓core͔nsnp 2 4 P e states in Mg − ͑n =3͒ and Ca − ͑n =4͒ negative ions in the photon energy range =0-10 eV. Double-ionization thresholds for Mg II and Ca II as well as doubly excited thresholds of the residual atoms Mg I and Ca I are located within the photon energy range considered and thus doubly and triply excited states of both Mg − and Ca − are reached. We use a complex scaled configuration interaction ͑CSCI͒ method for the three active electrons supplemented with a sophisticated model potential as developed by Laughlin ͓Phys. Scr. 45, 238 ͑1992͔͒ to account for core-valence interactions. The CI calculations are based on Mg + and Ca + one-electron orbitals expanded in terms of B-spline basis set. We compare our cross sections with the only calculation available up to a photon energy 0.25 Ry ͑ ϳ 3.4 eV͒ ͓Zeng et al., Phys. Rev. A 62, 022713 ͑2000͔͒ performed by using the R-matrix method, in which only one 4 P o resonance for Mg − and two ͑ 4 P o and 4 D o ͒ for Ca − were predicted. In this work, by analyzing both the cross sections and the locations of the S-matrix poles in the complex plane, we are able to predict six 4 P o , four 4 D o , and four 4 S o resonant states for Mg − , and three 4 P o and two 4 D o resonant states in Ca − .
Physical Review A, 2010
Two-photon double ionization (TPDI) of D 2 is studied for 38-eV photons at the Free Electron Lase... more Two-photon double ionization (TPDI) of D 2 is studied for 38-eV photons at the Free Electron Laser in Hamburg (FLASH). Based on model calculations, instantaneous and sequential absorption pathways are identified as separated peaks in the measured D + + D + fragment kinetic energy release (KER) spectra. The instantaneous process appears at high KER, corresponding to ionization at the molecule's equilibrium distance, in contrast to sequential ionization mainly leading to low-KER contributions. Measured fragment angular distributions are in good agreement with theory.
Nature, 2010
The development of attosecond laser pulses allows one to probe the inner workings of atoms and mo... more The development of attosecond laser pulses allows one to probe the inner workings of atoms and molecules on the timescale of the electronic response 1-4. In molecules, attosecond pump-probe spectroscopy enables investigations of the prompt charge redistribution and localization that accompany photo-excitation processes, where a molecule is lifted from the ground Born-Oppenheimer potential energy surface to one or more excited surfaces, and where subsequent photochemistry evolves on femtosecond timescales. Here we present the first example of a molecular
Journal of Physics B: Atomic, Molecular and Optical Physics, 2009
We have measured the production of both Lyα and Hα fluorescence from atomic H and D for the photo... more We have measured the production of both Lyα and Hα fluorescence from atomic H and D for the photodissociation of H 2 and D 2 by linearly polarized photons with energies between 24 and 60 eV. In this energy range, excited photofragments result primarily from the production of doubly excited molecular species which promptly autoionize or dissociate into two neutrals. Our data are compared with ab initio calculations of the dissociation process, in which both doubly excited state production and prompt ionization (nonresonant) channels are considered. Agreement between our experimental data and that of earlier work, and with our theoretical calculations, is qualitative at best.
Home Search Collections Journals About Contact us My IOPscience You may also be interested in: Ti... more Home Search Collections Journals About Contact us My IOPscience You may also be interested in: Time-resolved resonant photoionization of He using a time-dependent Feshbach method with ultrashort laser pulses C M Granados-Castro and J L Sanz-Vicario Time-resolved resonant photoionization of He using a time-dependent Feshbach method with ultrashort laser pulses C M Granados-Castro and J L Sanz-Vicario Reply to comment on 'Time-resolved resonant photoionization of He using a time-dependent Feshbach method with ultrashort laser pulses'
Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licenc... more Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.
ABSTRACT We study the resonant photoionization of the Helium atom subject to ultrashort laser pul... more ABSTRACT We study the resonant photoionization of the Helium atom subject to ultrashort laser pulses by using a Feshbach formalism in the time domain. We solve the projected time-dependent Schrodinger equation in terms of a configuration interaction spectral method, with a total wave function expanded with configurations defined within bound-like ( ##IMG## [http://ej.iop.org/images/1742-6596/488/3/032023/jpconf14_488_032023_eqn001.gif] ) and scattering-like ( ##IMG## [http://ej.iop.org/images/1742-6596/488/3/032023/jpconf14_488_032023_eqn002.gif] ) halfspaces. The method allows for accurate descriptions of both the atomic structure (energy positions and widths) as well as for the resonant photodynamics using ultrashort laser pulses. Special attention is given to the temporal formation of Fano profiles in the one- and two-photon ionization cross sections.
The presence of net circular dichroism in the photoionization of nonchiral homonuclear molecules ... more The presence of net circular dichroism in the photoionization of nonchiral homonuclear molecules has been put in evidence recently through the measurement of molecular-frame photoelectron angular distributions in dissociative photoionization of H 2 [Dowek et al., Phys. Rev. Lett. 104, 233003 (2010)]. In this work we present a detailed study of circular dichroism in the photoelectron angular distributions of H 2 and D 2 molecules, oriented perpendicularly to the propagation vector of the circularly polarized light, at different photon energies (20, 27, and 32.5 eV). Circular dichroism in the angular distributions at 20 and to a large extent 27 eV exhibits the usual pattern in which inversion symmetry is preserved. In contrast, at 32.5 eV, the inversion symmetry breaks down, which eventually leads to total circular dichroism after integration over the polar emission angle. Time-dependent ab initio calculations support and explain the observed results for H 2 in terms of quantum interferences between direct photoionization and delayed autoionization from the Q 1 and Q 2 doubly excited states into ionic states (1sσ g and 2pσ u) of different inversion symmetry. Nevertheless, for D 2 at 32.5 eV, there is a particular case where theory and experiment disagree in the magnitude of the symmetry breaking: when D + ions are produced with an energy of around 5 eV. This reflects the subleties associated to such simple molecules when exposed to this fine scrutiny.
Synopsis Shannon entropies and Fisher information calculated from one-particle density distributi... more Synopsis Shannon entropies and Fisher information calculated from one-particle density distributions and von Neumann and linear entropies (the latter two as a measure of entanglement) computed from the reduced oneparticle density matrix are analyzed for the 1,3 S e , 1,3 P o and 1,3 D e Rydberg series of He doubly excited states below the second ionization threshold. We find that both Fisher information and entanglement measures are able to discriminate resonances pertaining to different (K, T) A series.
Physical review letters, Jan 22, 2011
We report experiments where hydrogen molecules were dissociatively ionized by an attosecond pulse... more We report experiments where hydrogen molecules were dissociatively ionized by an attosecond pulse train in the presence of a near-infrared field. Fragment ion yields from distinguishable ionization channels oscillate with a period that is half the optical cycle of the IR field. For molecules aligned parallel to the laser polarization axis, the oscillations are reproduced in two-electron quantum simulations, and can be explained in terms of an interference between ionization pathways that involve different harmonic orders and a laser-induced coupling between the 1sσ(g) and 2pσ(u) states of the molecular ion. This leads to a situation where the ionization probability is sensitive to the instantaneous polarization of the molecule by the IR electric field and demonstrates that we have probed the IR-induced electron dynamics with attosecond pulses.
Physical Review a, 2003
We report calculated photodetachment cross sections from the metastable Be Ϫ 1s 2 2s2p 2 4 P e st... more We report calculated photodetachment cross sections from the metastable Be Ϫ 1s 2 2s2p 2 4 P e state in the photon energy range 0-10 eV. Outer-shell photodetachment takes place in this energy range, which includes the double-ionization threshold Be ϩ (2 S e) at ϳ7 eV as well as doubly excited thresholds of the residual atom up to the Be(1s 2 2p4 f) threshold at ϳ10 eV. Therefore, triply excited states of Be Ϫ are reached within the selected photon energy. We have implemented the complex scaled configuration interaction method along with a model potential for the 1s 2 core to uncover the first series of Be Ϫ 4 L o resonant states. In this work, four 4 P o , seven 4 D o , and two 4 S o resonances are reported and we compare our cross section with other previous theoretical calculations, that reported none or, at most, two resonances.
Physical Review Letters, 2010
Circular dichroism is a consequence of chirality. However, nonchiral molecules can also exhibit i... more Circular dichroism is a consequence of chirality. However, nonchiral molecules can also exhibit it when the measurement itself introduces chirality, e.g., when measuring molecular-frame photoelectron angular distributions. The few such experiments performed on homonuclear diatomic molecules show that, as expected, circular dichroism vanishes when the molecular-frame photoelectron angular distributions are integrated over the polar electron emission angle. Here we show that this is not the case in resonant dissociative ionization of H 2 for photons of 30-35 eV, which is the consequence of the delayed ionization from molecular doubly excited states into ionic states of different inversion symmetry.
Physical Review A, 2006
We present a nonperturbative time-dependent theoretical method to study H 2 ionization with femto... more We present a nonperturbative time-dependent theoretical method to study H 2 ionization with femtosecond laser pulses when the photon energy is large enough to populate the Q 1 ͑25-28 eV͒ and Q 2 ͑30-37 eV͒ doubly excited autoionizing states. We have investigated the role of these states in dissociative ionization of H 2 and analyzed, in the time domain, the onset of the resonant peaks appearing in the proton kinetic energy distribution. Their dependence on photon frequency and pulse duration is also analyzed. The results are compared with available experimental data and with previous theoretical results obtained within a stationary perturbative approach. The method allows us as well to obtain dissociation yields corresponding to the decay of doubly excited states into two H atoms. The calculated H͑n =2͒ yields are in good agreement with the experimental ones.
Physical Review A, 2010
Using a novel split-mirror setup attached to a Reaction Microscope at the Free electron LASer in ... more Using a novel split-mirror setup attached to a Reaction Microscope at the Free electron LASer in Hamburg (FLASH) we demonstrate an XUV-pump-XUV-probe
Physical Review A, 2009
Photoelectron angular distributions from fixed-in-space H 2 molecules exposed to ultrashort xuv l... more Photoelectron angular distributions from fixed-in-space H 2 molecules exposed to ultrashort xuv laser pulses have been evaluated. The theoretical method is based on the solution of the time-dependent Schrödinger equation in a basis of stationary states that include all electronic and vibrational degrees of freedom. Asymmetric angular distributions are observed as a consequence of the delayed ionization from the H 2 doubly excited states, which induces interferences between gerade and ungerade ionization channels. The analysis of this asymmetry as a function of pulse duration can provide an estimate of the corresponding autoionization widths.
Physical Review A, 2013
We have implemented a method based on the Feshbach formalism along with an explicitly correlated ... more We have implemented a method based on the Feshbach formalism along with an explicitly correlated configuration interaction method to perform a systematic study on the behavior of resonance parameters (energies and lifetimes) of the autoionizing states of plasma-embedded He 1,3 S e , 1,3 P o , and 1,3 D e , as a function of the screening strength. In particular, we study the evolution of the lowest states in the series located below the He + (N = 2) ionization threshold in the unscreened case. At variance with one-electron atoms (where shape resonance widths vary monotonically with the screening strength) the evolution of the Auger width with respect to screening is found to be different for each series represented by (K,T) A pseudoquantum numbers until resonances merge into the upper electronic continuum, when crossing the He + (2s) threshold. We conclude from our ab initio calculations that, although resonances pertaining to the same (K,T) A series share a similar tendency in their widths against the screening strength, general propensity rules for the robustness of lifetimes, based on the isomorphic series in the (K,T) A classification, cannot be established in plasma-embedded helium.
Physical Review A, 2002
The K-shell photodetachment of the metastable 1s2s2p 4 P o He - state is calculated ab initio wit... more The K-shell photodetachment of the metastable 1s2s2p 4 P o He - state is calculated ab initio with a complex scaled configuration interaction method in the photon energy region between the He 2s2p 3 P o threshold and the second double ionization threshold He + (n=2). ...
Physical Review A, 2002
The photodetachment of the metastable He Ϫ 1s2s2p 4 P o state has been calculated in two photon e... more The photodetachment of the metastable He Ϫ 1s2s2p 4 P o state has been calculated in two photon energy regions of interest: the first, named here as energy region I, below the double photoionization threshold He ϩ (nϭ1), involving outer-shell ionization and doubly excited states of He Ϫ , and the second, named here as region II, above the He Ϫ 1s ionization threshold and below the He ϩ (nϭ2) threshold, involving K-shell detachment and triply excited states of a He Ϫ ''hollow ion.'' We have implemented an ab initio three-electron configuration-interaction method in the LS-coupling scheme combined with complex scaling to obtain resonance positions and widths and the photodetachment cross sections. We have revisited region I, although widely studied before, as a test of our method. Notwithstanding some small discrepancies, our complex scaling results compare well with the previously published results and also add new understanding to some features in the cross section. Our emphasis is given to K-shell photodetachment in photon energy region II, where comparison is made with two other recent theoretical calculations that use completely different methods, and that were in dispute. We also compare with a very recent experiment for the He Ϫ K-shell photodetachment, which displays three major features; a broad nonresonant hump after the He 2s2p 3 P o threshold and two other peaks. A complex scaling analysis of prominent structures in the photodetachment spectra in region II, previously claimed to be nonresonant structures, leads to a different conclusion; i.e., they are all true triply excitedstate resonances, and two of them correspond to the peaks observed experimentally.
Physical Review A, 2008
We report on calculated outer-shell photodetachment cross sections from the metastable ͓core͔nsnp... more We report on calculated outer-shell photodetachment cross sections from the metastable ͓core͔nsnp 2 4 P e states in Mg − ͑n =3͒ and Ca − ͑n =4͒ negative ions in the photon energy range =0-10 eV. Double-ionization thresholds for Mg II and Ca II as well as doubly excited thresholds of the residual atoms Mg I and Ca I are located within the photon energy range considered and thus doubly and triply excited states of both Mg − and Ca − are reached. We use a complex scaled configuration interaction ͑CSCI͒ method for the three active electrons supplemented with a sophisticated model potential as developed by Laughlin ͓Phys. Scr. 45, 238 ͑1992͔͒ to account for core-valence interactions. The CI calculations are based on Mg + and Ca + one-electron orbitals expanded in terms of B-spline basis set. We compare our cross sections with the only calculation available up to a photon energy 0.25 Ry ͑ ϳ 3.4 eV͒ ͓Zeng et al., Phys. Rev. A 62, 022713 ͑2000͔͒ performed by using the R-matrix method, in which only one 4 P o resonance for Mg − and two ͑ 4 P o and 4 D o ͒ for Ca − were predicted. In this work, by analyzing both the cross sections and the locations of the S-matrix poles in the complex plane, we are able to predict six 4 P o , four 4 D o , and four 4 S o resonant states for Mg − , and three 4 P o and two 4 D o resonant states in Ca − .
Physical Review A, 2010
Two-photon double ionization (TPDI) of D 2 is studied for 38-eV photons at the Free Electron Lase... more Two-photon double ionization (TPDI) of D 2 is studied for 38-eV photons at the Free Electron Laser in Hamburg (FLASH). Based on model calculations, instantaneous and sequential absorption pathways are identified as separated peaks in the measured D + + D + fragment kinetic energy release (KER) spectra. The instantaneous process appears at high KER, corresponding to ionization at the molecule's equilibrium distance, in contrast to sequential ionization mainly leading to low-KER contributions. Measured fragment angular distributions are in good agreement with theory.
Nature, 2010
The development of attosecond laser pulses allows one to probe the inner workings of atoms and mo... more The development of attosecond laser pulses allows one to probe the inner workings of atoms and molecules on the timescale of the electronic response 1-4. In molecules, attosecond pump-probe spectroscopy enables investigations of the prompt charge redistribution and localization that accompany photo-excitation processes, where a molecule is lifted from the ground Born-Oppenheimer potential energy surface to one or more excited surfaces, and where subsequent photochemistry evolves on femtosecond timescales. Here we present the first example of a molecular
Journal of Physics B: Atomic, Molecular and Optical Physics, 2009
We have measured the production of both Lyα and Hα fluorescence from atomic H and D for the photo... more We have measured the production of both Lyα and Hα fluorescence from atomic H and D for the photodissociation of H 2 and D 2 by linearly polarized photons with energies between 24 and 60 eV. In this energy range, excited photofragments result primarily from the production of doubly excited molecular species which promptly autoionize or dissociate into two neutrals. Our data are compared with ab initio calculations of the dissociation process, in which both doubly excited state production and prompt ionization (nonresonant) channels are considered. Agreement between our experimental data and that of earlier work, and with our theoretical calculations, is qualitative at best.