| 1. |
- Dong, Xiao Xia, et al.
(författare)
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Carrier-envelope-phase measurement of sub-cycle UV pulses using angular photofragment distributions
- 2022
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Ingår i: Communications Physics. - : Springer Nature. - 2399-3650. ; 5:1
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Tidskriftsartikel (refereegranskat)abstract
- Carrier-envelope-phase (CEP) of sub-cycle ultraviolet (UV) pulse strongly influences the dynamics of quantum systems, but its characterization is not accessible experimentally. Here we investigate photodissociation of a diatomic molecule from its ground-rovibrational state in a linearly polarized weak sub-cycle UV pulse with a controlled CEP. The angular distribution of photofragments shows an asymmetric profile deviating from the well-known cos(2-) or sin(2)-like ones, which can be identified as a way to imprint CEP. We unveil that such an effect stems from the temporal neighboring rotational excitation by molecular permanent dipole interaction through the joint contributions between counter-rotating and rotating terms. This in turn, opens different pathways in photodissociation dynamics. Given that the temporal excitation between various states with close energies can be manipulated by CEP of subcycle UV pulses, our results pave ways for understanding and manipulating electron, nuclear and their joint dynamics with variation of CEP of attosecond pulses.
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| 2. |
- Ertan, Emelie, 1988-
(författare)
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Quantum chemical calculations of multidimensional dynamics probed in resonant inelastic X-ray scattering
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis is devoted to the theoretical study of the dynamical processes induced by light-matter interactions in molecules and molecular systems. To this end, the multidimensional nuclear dynamics probed in resonant inelastic X-ray scattering (RIXS) of small molecules, exemplified by H2O (g) and H2S (g), as well as more complex molecular systems, exemplified by NH3 (aq) and kaolinite clay, are modelled. The computational methodology consists of a combination of ab initio quantum chemistry calculations, quantum nuclear wave packet dynamics and in certain cases molecular dynamics modelling. This approach is used to simulate K-edge RIXS spectra and the theoretical results are evaluated against experimental measurements.Specifically, the vibrational profile for decay back to the electronic ground state of the H2O molecule displays a vibrational selectivity introduced by the dynamics in the core-excited state. Simulation of the inelastic decay channel to the electronic |1b1-1,4a11> valence-excited state shows that the splitting of the spectral profile arises from the contribution of decay in the OH fragment. The character of the S1s-1 and S2p-1 core-excited states of the H2S molecule has been investigated and distinct similarities and differences with the H2O molecule have been identified. RIXS has also been used as a probe of the hydrogen bonding environment in aqueous ammonia and by detailed analysis of the valence orbitals of NH3 and water, the spectral profiles are explained. Finally, it is shown that vibrations of weakly hydrogen bonding OH are excited in RIXS decay to the electronic ground state in kaolinite.
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| 3. |
- Liu, Yan Rong, et al.
(författare)
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Electron-rotation coupling in diatomics under strong-field excitation
- 2020
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Ingår i: Physical Review A: covering atomic, molecular, and optical physics and quantum information. - : American Physical Society. - 2469-9926 .- 2469-9934. ; 102:3
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Tidskriftsartikel (refereegranskat)abstract
- The photoexcitation and photodissociation of diatomic molecules by intense pulse lasers has been the subject of extensive investigations over the past decades. However, the usually employed theoretical framework neglects the coupling between the molecular rotational angular momentum (R) and the angular momentum of the electrons projected onto the molecular axis Omega = Lambda + Sigma, which results in the known Lambda-doubling phenomenon in high-resolution electronic spectra of diatomic molecules. While neglecting this coupling is an excellent approximation in the weak-field or perturbative regime owing to the large mass difference between the rotating atoms and the electrons, the approximation breaks down for intense laser pulses because of the repeated Rabi cycling of the electronic transitions, which can have a significant effect on the rotational degrees of freedom of the molecule. By correcting the transition dipole matrix elements and introducing angular basis sets based on Wigner D functions, the conventional theoretical treatment is generalized to a universal description valid for both the weak- and strong-field regimes. The theoretical treatment developed here is applied to the vertical bar(1)Sigma > to vertical bar(1)Pi > transitions in diatomic systems. Our results reveal that, for field intensities resulting in about one Rabi cycling for extreme ultraviolet or x-ray transitions, the theoretical predictions by the conventional theoretical frame need to be corrected when considering observables such as the molecular alignment and the angular distribution of the photofragments.
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| 4. |
- Liu, Yan Rong, et al.
(författare)
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Electron-rotation coupling in UV photodissociation of aligned diatomics
- 2022
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Ingår i: Physical Review Research. - : American Physical Society (APS). - 2643-1564. ; 4:1
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the effect of electron-rotation coupling (R -Omega coupling) on fs UV photodissociation dynamics of aligned diatomic molecules. We consider the showcase of ground-state MeH+ ((1)Sigma(+)) pumped by an fs IR pulse, which initiates rotational dynamics leading to field-free molecular alignment. A time-delayed fs UV pulse probes the degree of alignment of the rotational wave packet in the framework of photodissociation spectroscopy. The molecular alignment correlates directly with the angular distribution of the photofragments in the dissociative (1)Pi state, as it is shown in our simulations comparing the cases when the R -Omega coupling is included and ignored. We show how the angular distribution of the photofragment is strongly affected by the R -Omega coupling at various delay times with specific molecular alignment. It was shown that increases of the fs UV pulse intensity and the degree of alignment enhance the effect of R -Omega coupling on the angular distribution of the photofragments. On the contrary, an increase of the initial temperature tends to reduce the effect of R -Omega coupling, which is explained by the fact that such an effect turns smaller as the increasing of magnetic state vertical bar M-0 vertical bar for each initial rotational state J(0); furthermore, higher excited rotational state J(0) contains more magnetic states M-0, and the results have been averaged over all degenerated M-0 states.
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| 5. |
- Liu, Yan Rong, et al.
(författare)
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Photodissociation dynamics of the NH molecule under intense VUV pulses
- 2020
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Ingår i: Physical Review Research. - : American Physical Society (APS). - 2643-1564. ; 2:4
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Tidskriftsartikel (refereegranskat)abstract
- Photodissociation dynamics of the NH molecule excited from the triplet ground X-3 Sigma(-) to 2(3)Pi state by resonant intense VUV pulses have been comprehensively investigated by the recently proposed theoretical treatment involving the electron-rotation coupling. The rotational dynamics are described by the Wigner D functions, and the electronic transition operators are refined with respect to the changes of the projection of the total orbital angular momentum onto the molecular axis Delta Lambda. The kinetic energy release (KER) spectra and the angular distribution of photofragments are obtained by averaging over nine degenerate initial angular states, computed separately. We have shown that the KER spectra are not very sensitive to the electron-rotation coupling for different pulse intensity and energy detuning from the resonance. The angular distribution of the photofragments, on the contrary, is strongly affected by the electron-rotation coupling at the small angles between the molecular axis and laser polarization. The influence of the electron-rotational coupling shows different trends for positive and negative detunings from the resonance at variation of the pulse intensity, which is explained by sufficient changes of the rotational wave packet dynamics caused by different phases of the initial rotational states.
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| 6. |
- Liu, Yan Rong, et al.
(författare)
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Photodissociation spectroscopy via a rovibrational resonance in intense UV pulses
- 2022
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Ingår i: Physical Review Research. - : American Physical Society (APS). - 2643-1564. ; 4:4
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Tidskriftsartikel (refereegranskat)abstract
- Photodissociation dynamics via a rovibrational resonance in intense UV pulses is investigated theoretically, using a showcase CH+ molecule promoted to the C 1E+ valence excited electronic state with a potential barrier, thus giving access to study shape resonance controlled by the pulse frequency. Simulations of the kinetic energy release (KER) and angular distribution of the photofragments (ADP) spectra show dramatic differences for the cases when the pulse is tuned on and off the rovibrational resonance. It shows that as the increasing pulse intensity for the transitions to shape resonance, the KER spectra develop into new and higher energy peaks overlying on the broadened background, which is explained by the involvement of other resonances with higher partial waves through electronic Rabi flopping between the ground and excited electronic states. Those nonlinear contribution increases drastically the probability of photofragmentation along the laser polarization in the ADP spectra. The coincident KER-ADP spectra reveal clearly the correlated dynamics in the vicinity of the dissociation barrier. The present work opens possibilities for the manipulation of ultrafast photodissociation dynamics with the help of resonance states in the continuum.
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| 7. |
- Liu, Yan Rong, et al.
(författare)
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Ultraviolet Pump-Probe Photodissociation Spectroscopy of Electron-Rotation Coupling in Diatomics
- 2021
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Ingår i: The Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 12:23, s. 5534-5539
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Tidskriftsartikel (refereegranskat)abstract
- The electronic angular momentum projected onto the diatomic axis couples with the angular momentum of the nuclei, significantly affecting the rotational motion of the system under electronic excitations by intense lasers. In this letter, we propose a pump-probe photodissociation scheme for an accurate determination of electron-rotation coupling effects induced by the strong fields. As a showcase we study the CH+ molecule excited by a short intense ultraviolet pump pulse to the A(1)Pi state, which triggers coupled rovibrational dynamics. The dynamics is observed by measuring the kinetic energy release and angular resolved photofragmentation upon photodissociation induced by the time-delayed probe pulse populating the C-1 Sigma(+) state. Simulations of the rovibrational dynamics unravel clear fingerprints of the electron-rotation coupling effects that can be observed experimentally. The proposed pump-probe scheme opens new possibilities for the study of ultrafast dynamics following valence electronic transitions with current laser technology, and possible applications are also discussed.
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| 8. |
- Wang, Chao, et al.
(författare)
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Rebuilding the vibrational wavepacket in TRAS using attosecond X-ray pulses
- 2024
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Ingår i: Communications Physics. - : Springer Nature. - 2399-3650. ; 7:1
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Tidskriftsartikel (refereegranskat)abstract
- Time-resolved X-ray photoelectron spectroscopy (TXPS) is a well-established technique to probe coherent nuclear wavepacket dynamics using both table-top and free-electron-based ultrafast X-ray lasers. Energy resolution, however, becomes compromised for a very short pulse duration in the sub-femtosecond range. By resonantly tuning the X-ray pulse to core-excited states undergoing Auger decay, this drawback of TXPS can be mitigated. While resonant Auger-electron spectroscopy (RAS) can recover the vibrational structures not hidden by broadband excitation, the full reconstruction of the wavepacket is a standing challenge. Here, we theoretically demonstrate how the complete information of a nuclear wavepacket, i.e., the populations and relative phases of the vibrational states constituting the wavepacket, can be retrieved from time-resolved RAS (TRAS) measurements. Thus, TRAS offers key insights into coupled nuclear and electronic dynamics in complex systems on ultrashort timescales, providing an alternative to leverage femtosecond and attosecond X-ray probe pulses.
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| 9. |
- Wang, Chao, et al.
(författare)
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Time-Resolved Resonant Auger Scattering Clocks Distortion of a Molecule
- 2023
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Ingår i: The Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 14:24, s. 5475-5480
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Tidskriftsartikel (refereegranskat)abstract
- Resonant Auger scattering (RAS) provides information on the core-valence electronic transition and impresses a rich fingerprint of the electronic structure and nuclear configuration at the time-initiating RAS process. Here, we suggest using a femtosecond X-ray pulse to trigger RAS in a distorted molecule, which is generated from the nuclear evolution on a valence excited state pumped by a femtosecond ultraviolet pulse. With the time delay varied, the amount of molecular distortion can be controlled and the RAS measurements imprint both their electronic structures and changing geometries. This strategy is showcased in H2O prepared in an O-H dissociative valence state, where molecular and fragment lines appear in RAS spectra as signatures of ultrafast dissociation. Given the generality of this approach for a broad class of molecules, this work opens a new alternative pump-probe technique for mapping the core and valence dynamics with ultrashort X-ray probe pulses.
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