| 1. |
- Sanchez-Gonzalez, A., et al.
(author)
-
Auger electron and photoabsorption spectra of glycine in the vicinity of the oxygen K-edge measured with an X-FEL
- 2015
-
In: Journal of Physics B-Atomic Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 48:23
-
Journal article (peer-reviewed)abstract
- We report the first measurement of the near oxygen K-edge auger spectrum of the glycine molecule. Our work employed an x-ray free electron laser as the photon source operated with input photon energies tunable between 527 and 547 eV. Complete electron spectra were recorded at each photon energy in the tuning range, revealing resonant and non-resonant auger structures. Finally ab initio theoretical predictions are compared with the measured above the edge auger spectrum and an assignment of auger decay channels is performed.
|
|
| 2. |
- Gryzlova, E. V., et al.
(author)
-
Doubly resonant three-photon double ionization of Ar atoms induced by an EUV free-electron laser
- 2011
-
In: Physical Review A (Atomic, Molecular and Optical Physics). - 1050-2947. ; 84:6
-
Journal article (peer-reviewed)abstract
- A mechanism for three-photon double ionization of atoms by extreme-ultraviolet free-electron laser pulses is revealed, where in a sequential process the second ionization step, proceeding via resonant two-photon ionization of ions, is strongly enhanced by the excitation of ionic autoionizing states. In contrast to the conventional model, the mechanism explains the observed relative intensities of photoelectron peaks and their angular dependence in three-photon double ionization of argon.
|
|
| 3. |
- Iablonskyi, D., et al.
(author)
-
Slow Interatomic Coulombic Decay of Multiply Excited Neon Clusters
- 2016
-
In: Physical Review Letters. - 0031-9007. ; 117:27
-
Journal article (peer-reviewed)abstract
- Ne clusters (∼5000 atoms) were resonantly excited (2p→3s) by intense free electron laser (FEL) radiation at FERMI. Such multiply excited clusters can decay nonradiatively via energy exchange between at least two neighboring excited atoms. Benefiting from the precise tunability and narrow bandwidth of seeded FEL radiation, specific sites of the Ne clusters were probed. We found that the relaxation of cluster surface atoms proceeds via a sequence of interatomic or intermolecular Coulombic decay (ICD) processes while ICD of bulk atoms is additionally affected by the surrounding excited medium via inelastic electron scattering. For both cases, cluster excitations relax to atomic states prior to ICD, showing that this kind of ICD is rather slow (picosecond range). Controlling the average number of excitations per cluster via the FEL intensity allows a coarse tuning of the ICD rate.
|
|
| 4. |
- Ma, R., et al.
(author)
-
Photoelectron angular distributions for the two-photon ionization of helium by ultrashort extreme ultraviolet free-electron laser pulses
- 2013
-
In: Journal of Physics B: Atomic, Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 46:16
-
Journal article (peer-reviewed)abstract
- 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.
|
|
| 5. |
- Mondal, S., et al.
(author)
-
Photoelectron angular distributions for the two-photon sequential double ionization of xenon by ultrashort extreme ultraviolet free electron laser pulses
- 2013
-
In: Journal of Physics B: Atomic, Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 46:16
-
Journal article (peer-reviewed)abstract
- 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.
|
|
| 6. |
- Rouzee, A., et al.
(author)
-
Angle-resolved photoelectron spectroscopy of sequential three-photon triple ionization of neon at 90.5 eV photon energy
- 2011
-
In: Physical Review A (Atomic, Molecular and Optical Physics). - 1050-2947. ; 83:3
-
Journal article (peer-reviewed)abstract
- Multiple photoionization of neon atoms by a strong 13.7 nm (90.5 eV) laser pulse has been studied at the FLASH free electron laser in Hamburg. A velocity map imaging spectrometer was used to record angle-resolved photoelectron spectra on a single-shot basis. Analysis of the evolution of the spectra with the FEL pulse energy in combination with extensive theoretical calculations allows the ionization pathways that contribute to be assigned, revealing the occurrence of sequential three-photon triple ionization.
|
|
| 7. |
- Rouzee, A., et al.
(author)
-
Towards imaging of ultrafast molecular dynamics using FELs
- 2013
-
In: Journal of Physics B: Atomic, Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 46:16
-
Journal article (peer-reviewed)abstract
- The dissociation dynamics induced by a 100 fs, 400 nm laser pulse in a rotationally cold Br-2 sample was characterized by Coulomb explosion imaging (CEI) using a time-delayed extreme ultra-violet (XUV) FEL pulse, obtained from the Free electron LASer in Hamburg (FLASH). The momentum distribution of atomic fragments resulting from the 400 nm-induced dissociation was measured with a velocity map imaging spectrometer and used to monitor the internuclear distance as the molecule dissociated. By employing the simultaneously recorded in-house timing electro-optical sampling data, the time resolution of the final results could be improved to 300 fs, compared to the inherent 500 fs time-jitter of the FEL pulse. Before dissociation, the Br-2 molecules were transiently 'fixed in space' using laser-induced alignment. In addition, similar alignment techniques were used on CO2 molecules to allow the measurement of the photoelectron angular distribution (PAD) directly in the molecular frame (MF). Our results on MFPADs in aligned CO2 molecules, together with our investigation of the dissociation dynamics of the Br-2 molecules with CEI, show that information about the evolving molecular structure and electronic geometry can be retrieved from such experiments, therefore paving the way towards the study of complex non-adiabatic dynamics in molecules through XUV time-resolved photoion and photoelectron spectroscopy.
|
|
| 8. |
- Takanashi, T, et al.
(author)
-
Time-Resolved Measurement of Interatomic Coulombic Decay Induced by Two-Photon Double Excitation of Ne2
- 2017
-
In: Physical Review Letters. - 0031-9007. ; 118:3
-
Journal article (peer-reviewed)abstract
- The hitherto unexplored two-photon doubly excited states [Ne∗(2p-13s)]2 were experimentally identified using the seeded, fully coherent, intense extreme ultraviolet free-electron laser FERMI. These states undergo ultrafast interatomic Coulombic decay (ICD), which predominantly produces singly ionized dimers. In order to obtain the rate of ICD, the resulting yield of Ne2+ ions was recorded as a function of delay between the extreme ultraviolet pump and UV probe laser pulses. The extracted lifetimes of the long-lived doubly excited states, 390(-130/+450) fs, and of the short-lived ones, less than 150 fs, are in good agreement with ab initio quantum mechanical calculations.
|
|
| 9. |
- Iablonskyi, D., et al.
(author)
-
Interatomic Coulombic Decay Processes after Multiple Valence Excitations in Ne Clusters
- 2015
-
In: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6596 .- 1742-6588. ; 635, s. 112067-112067
-
Conference paper (peer-reviewed)abstract
- We present a comprehensive analysis of autoionization processes in Ne clusters (similar to 5000 atoms) after multiple valence excitations by free electron laser radiation. The evolution from 2-body interatomic Coulombic decay (ICD) to 3-body ICD is demonstrated when changing from surface to bulk Frenkel exciton excitation. Super Coster-Kronig type 2-body ICD is observed at Wannier exciton which quenches the main ICD channel.
|
|
| 10. |
- Kukk, E., et al.
(author)
-
Formative period in the x-ray-induced photodissociation of organic molecules
- 2021
-
In: Physical Review Research. - 2643-1564. ; 3:1
-
Journal article (peer-reviewed)abstract
- Absorption of x-ray photons by atomic inner shells of light-element organics and biomolecules often leads to formation of dicationic electronic states and to molecular fragmentation. We investigated the x-ray-induced dissociation landscape of a representative medium-sized organic molecule, thiophene, by femtosecond x-ray pulses from the Super Photon Ring-8 GeV (SPring-8) Angstrom Compact Free-Electron Laser (SACLA). Holes, created in the sulfur 2p orbital by photoemission, were filled by the Auger process that created dicationic molecular states within a broad range of internal energies—a starting point particular to x-ray-induced dynamics. The evolution of the ionized molecules was monitored by a pump-probe experiment using a near-infrared (800 nm) laser pulse. Ion-ion coincidence and ion momentum analysis reveals enhanced yields of ionic fragments from multibody breakup of the ring, attributed to additional ionization of the highly excited fraction of the dicationic parent molecular states. The transient nature of the enhancement and its decay with about a 160-fs time constant indicate formation of an open-ring parent geometry and the statistical survival time of the parent species before the dissociation events. By probing specific Auger final states of transient, highly excited nature by near-infrared light, we demonstrate how pump-probe signatures can be related to the key features in dynamics during the early period of the x-ray-induced damage of organic molecules and biomolecules.
|
|
