The Experts below are selected from a list of 26097 Experts worldwide ranked by ideXlab platform
Uwe Thumm - One of the best experts on this subject based on the ideXlab platform.
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steering the Nuclear Motion in singly ionized argon dimers with mutually detuned laser pulses
Physical Review Letters, 2013Co-Authors: Maia Magrakvelidze, A Vredenborg, Ph L H Schmidt, T Jahnke, A Czasch, R Dorner, Uwe ThummAbstract:We demonstrate that the vibrational Nuclear Motion of singly ionized argon dimers can be controlled with two ultrashort laser pulses of different wavelengths. In particular, we observe a striking ‘‘gap’’ in the pump-probe-delay-dependent kinetic-energy release spectrum only if the probe-pulse wavelength exceeds the pump-pulse wavelength. This ‘‘frustrated dissociation effect’’ is reproduced by our two-state quantum mechanical model, validating its interpretation as a pump-pulse-initiated population transfer between dipole-coupled Born-Oppenheimer electronic states of the dissociating Ar 2 þ molecular ion. Our numerical results also reproduce the measured collapse and fractional revival of the oscillating Ar 2 þ Nuclear wave packet, and, for single-pulse dissociation, the decrease of the kinetic-energy release with increasing laser wavelength.
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strong field modulated diffraction effects in the correlated electron Nuclear Motion in dissociating h 2
Physical Review Letters, 2008Co-Authors: Andreas Becker, Uwe ThummAbstract:We show that the electronic dynamics in a molecule driven by a strong field is complex and potentially even counterintuitive. As a prototype example, we simulate the interaction of a dissociating H2+ molecule with an intense infrared laser pulse. Depending on the laser intensity, the direction of the electron's Motion between the two nuclei is found to follow or oppose the classical laser-electric force. We explain the sensitive dependence of the correlated electronic-Nuclear Motion in terms of the diffracting electronic momentum distribution of the dissociating two-center system. The distribution is dynamically modulated by the Nuclear Motion and periodically shifted in the oscillating infrared electric field.
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Strong-field modulated diffraction effects in the correlated electron-Nuclear Motion in dissociating H(2+).
Physical review letters, 2008Co-Authors: Andreas Becker, Uwe ThummAbstract:We show that the electronic dynamics in a molecule driven by a strong field is complex and potentially even counterintuitive. As a prototype example, we simulate the interaction of a dissociating H2+ molecule with an intense infrared laser pulse. Depending on the laser intensity, the direction of the electron's Motion between the two nuclei is found to follow or oppose the classical laser-electric force. We explain the sensitive dependence of the correlated electronic-Nuclear Motion in terms of the diffracting electronic momentum distribution of the dissociating two-center system. The distribution is dynamically modulated by the Nuclear Motion and periodically shifted in the oscillating infrared electric field.
Lars Bojer Madsen - One of the best experts on this subject based on the ideXlab platform.
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Nuclear-Motion effects in attosecond transient-absorption spectroscopy of molecules
Physical Review A, 2015Co-Authors: Jens E. Bækhøj, Lun Yue, Lars Bojer MadsenAbstract:We investigate the characteristic effects of Nuclear Motion on attosecond transient absorption spectra in molecules by calculating the spectrum for different model systems. Two models of the hydrogen molecular ion are considered: one where the interNuclear separation is fixed, and one where the nuclei are free to vibrate. The spectra for the fixed nuclei model are similar to atomic spectra reported elsewhere, while the spectra obtained in the model including Nuclear Motion are very different and dominated by extremely broad absorption features. These broad absorption features are analyzed and their relation to molecular dissociation investigated. The study of the hydrogen molecular ion validates an approach based on the Born-Oppenheimer approximation and a finite electronic basis. This latter approach is then used to study the three-dimensional hydrogen molecule including Nuclear vibration. The spectrum obtained from H$_2$ is compared to the result of a fixed-nuclei calculation. In the attosecond transient absorption spectra of H$_2$ including Nuclear Motion we find a rich absorption structure corresponding to population of different vibrational states in the molecule, while the fixed-nuclei spectra again are very similar to atomic spectra. We find that light-induced structures at well-defined energies reported in atomic systems are also present in our fixed nuclei molecular spectra, but suppressed in the ${\text{H}_2}^+$ and H$_2$ spectra with moving nuclei. We show that the signatures of light-induced structures are closely related to the Nuclear dynamics of the system through the shapes and relative arrangement of the Born-Oppenheimer potential energy curves.
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High-order harmonic generation from polyatomic molecules including Nuclear Motion and a Nuclear modes analysis
Physical Review A, 2010Co-Authors: C. B. Madsen, Mahmoud Abu-samha, Lars Bojer MadsenAbstract:We present a generic approach for treating the effect of Nuclear Motion in high-order harmonic generation from polyatomic molecules. Our procedure relies on a separation of Nuclear and electron dynamics where we account for the electronic part using the Lewenstein model and Nuclear Motion enters as a Nuclear correlation function. We express the Nuclear correlation function in terms of Franck-Condon factors, which allows us to decompose Nuclear Motion into modes and identify the modes that are dominant in the high-order harmonic generation process. We show results for the isotopes CH{sub 4} and CD{sub 4} and thereby provide direct theoretical support for a recent experiment [S. Baker et al., Science 312, 424 (2006)] that uses high-order harmonic generation to probe the ultrafast structural Nuclear rearrangement of ionized methane.
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High-order harmonic generation from arbitrarily oriented diatomic molecules including Nuclear Motion and field-free alignment
Physical Review A, 2006Co-Authors: C. B. Madsen, Lars Bojer MadsenAbstract:We present a theoretical model of high-harmonic generation from diatomic molecules. The theory includes effects of alignment as well as Nuclear Motion and is used to predict results for N{sub 2}, O{sub 2}, H{sub 2}, and D{sub 2}. The results show that the alignment dependence of high-harmonics is governed by the symmetry of the highest occupied molecular orbital and that the inclusion of the Nuclear Motion in the theoretical description generally reduces the intensity of the harmonic radiation. We compare our model with experimental results on N{sub 2} and O{sub 2}, and obtain very good agreement.
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Strong-field ionization of diatomic molecules and companion atoms: Strong-field approximation and tunneling theory including Nuclear Motion
Physical Review A, 2005Co-Authors: Thomas Kim Kjeldsen, Lars Bojer MadsenAbstract:We present a detailed comparison of strong-field ionization of diatomic molecules and their companion atoms with nearly equal ionization potentials. We perform calculations in the length and velocity gauge formulations of the molecular strong-field approximation and with the molecular tunneling theory, and in both cases we consider effects of Nuclear Motion. A comparison of our results with experimental data shows that the length gauge strong-field approximation gives the most reliable predictions.
Michael A. Robb - One of the best experts on this subject based on the ideXlab platform.
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The Ehrenfest method with fully quantum Nuclear Motion (Qu-Eh): Application to charge migration in radical cations
The Journal of chemical physics, 2018Co-Authors: Andrew J. Jenkins, Morgane Vacher, K. Eryn Spinlove, Graham A. Worth, Michael A. RobbAbstract:An algorithm is described for quantum dynamics where an Ehrenfest potential is combined with fully quantum Nuclear Motion (Quantum-Ehrenfest, Qu-Eh). The method is related to the single-set variational multi-configuration Gaussian approach (vMCG) but has the advantage that only a single quantum chemistry computation is required at each time step since there is only a single time-dependent potential surface. Also shown is the close relationship to the “exact factorization method.” The quantum Ehrenfest method is compared with vMCG for study of electron dynamics in a modified bismethylene-adamantane cation system. Illustrative examples of electron-Nuclear dynamics are presented for a distorted allene system and for HCCI+ where one has a degenerate Π system.An algorithm is described for quantum dynamics where an Ehrenfest potential is combined with fully quantum Nuclear Motion (Quantum-Ehrenfest, Qu-Eh). The method is related to the single-set variational multi-configuration Gaussian approach (vMCG) but has the advantage that only a single quantum chemistry computation is required at each time step since there is only a single time-dependent potential surface. Also shown is the close relationship to the “exact factorization method.” The quantum Ehrenfest method is compared with vMCG for study of electron dynamics in a modified bismethylene-adamantane cation system. Illustrative examples of electron-Nuclear dynamics are presented for a distorted allene system and for HCCI+ where one has a degenerate Π system.
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Electron Dynamics upon Ionization of Polyatomic Molecules: Coupling to Quantum Nuclear Motion and Decoherence.
Physical review letters, 2017Co-Authors: Morgane Vacher, Michael J. Bearpark, Michael A. Robb, João Pedro MalhadoAbstract:Knowledge about the electronic Motion in molecules is essential for our understanding of chemical reactions and biological processes. The advent of attosecond techniques opens up the possibility to induce electronic Motion, observe it in real time, and potentially steer it. A fundamental question remains the factors influencing electronic decoherence and the role played by Nuclear Motion in this process. Here, we simulate the dynamics upon ionization of the polyatomic molecules paraxylene and modified bismethylene-adamantane, with a quantum mechanical treatment of both electron and Nuclear dynamics using the direct dynamics variational multiconfigurational Gaussian method. Our simulations give new important physical insights about the expected decoherence process. We have shown that the decoherence of electron dynamics happens on the time scale of a few femtoseconds, with the interplay of different mechanisms: the dephasing is responsible for the fast decoherence while the Nuclear overlap decay may actually help maintain it and is responsible for small revivals.
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Electron dynamics upon ionization: control of the timescale through chemical substitution and effect of Nuclear Motion.
The Journal of chemical physics, 2015Co-Authors: Morgane Vacher, Michael J. Bearpark, David Mendive-tapia, Michael A. RobbAbstract:Photoionization can generate a non-stationary electronic state, which leads to coupled electron-Nuclear dynamics in molecules. In this article, we choose benzene cation as a prototype because vertical ionization of the neutral species leads to a Jahn-Teller degeneracy between ground and first excited states of the cation. Starting with equal populations of ground and first excited states, there is no electron dynamics in this case. However, if we add methyl substituents that break symmetry but do not radically alter the electronic structure, we see charge migration: oscillations in the spin density that we can correlate with particular localized electronic structures, with a period depending on the gap between the states initially populated. We have also investigated the effect of Nuclear Motion on electron dynamics using a complete active space self-consistent field (CASSCF) implementation of the Ehrenfest method, most previous theoretical studies of electron dynamics having been carried out with fixed nuclei. In toluene cation for instance, simulations where the nuclei are allowed to move show significant differences in the electron dynamics after 3 fs, compared to simulations with fixed nuclei.
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Communication: oscillating charge migration between lone pairs persists without significant interaction with Nuclear Motion in the glycine and Gly-Gly-NH-CH3 radical cations.
The Journal of chemical physics, 2014Co-Authors: Morgane Vacher, Michael J. Bearpark, Michael A. RobbAbstract:Coupled electron-Nuclear dynamics has been studied, using the Ehrenfest method, for four conformations of the glycine molecule and a single conformation of Gly-Gly-NH-CH3. The initial electronic wavepacket was a superposition of eigenstates corresponding to ionization from the σ lone pairs associated with the carbonyl oxygens and the amine nitrogen. For glycine, oscillating charge migration (when the nuclei were frozen) was observed for the 4 conformers studied with periods ranging from 2 to 5 fs, depending on the energy gap between the lone pair cationic states. When coupled Nuclear Motion was allowed (which was mainly NH2 partial inversion), the oscillations hardly changed. For Gly-Gly-NH-CH3, charge migration between the carbonyl oxygens and the NH2 lone pair can be observed with a period similar to glycine itself, also without interaction with Nuclear Motion. These simulations suggest that charge migration between lone pairs can occur independently of the Nuclear Motion.
R Feifel - One of the best experts on this subject based on the ideXlab platform.
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Nuclear Motion driven by the Renner–Teller effect as observed in the resonant Auger decay to the X̃2Π electronic ground state of N2O+
The Journal of Chemical Physics, 2001Co-Authors: C Miron, M. Simon, Pascal Morin, S Nanbu, Nobuhiro Kosugi, S L Sorensen, M N Piancastelli, Olle Bjorneholm, A. Naves De Brito, R FeifelAbstract:High-resolution Auger spectroscopy applied under resonant Auger Raman conditions is shown to be a powerful tool for characterizing complex potential energy surfaces in core-excited systems. Using the example of Nt 1s–1*2 resonant Auger transition in nitrous oxide we emphasize the interplay between the Nuclear Motion and the electronic decay. We show how the choice of excitation energy allows selection of core-excited species of different geometries. The Nuclear dynamics of these species are mapped by measuring the resonant Auger decay spectra. In addition to the changes in vibrational structure observed for the resonant Auger decay spectra, a strong influence of Nuclear Motion on the electronic decay is revealed, inducing the so-called "dynamical Auger emission." The experimental results are supported by ab initio quantum chemical calculations restricted to a linear geometry of the core-excited state.
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Nuclear Motion driven by the renner teller effect as observed in the resonant auger decay to the x2π electronic ground state of n2o
Journal of Chemical Physics, 2001Co-Authors: C Miron, M. Simon, Pascal Morin, S Nanbu, Nobuhiro Kosugi, S L Sorensen, Naves A De Brito, M N Piancastelli, Olle Bjorneholm, R FeifelAbstract:High-resolution Auger spectroscopy applied under resonant Auger Raman conditions is shown to be a powerful tool for characterizing complex potential energy surfaces in core-excited systems. Using the example of Nt 1s–1*2 resonant Auger transition in nitrous oxide we emphasize the interplay between the Nuclear Motion and the electronic decay. We show how the choice of excitation energy allows selection of core-excited species of different geometries. The Nuclear dynamics of these species are mapped by measuring the resonant Auger decay spectra. In addition to the changes in vibrational structure observed for the resonant Auger decay spectra, a strong influence of Nuclear Motion on the electronic decay is revealed, inducing the so-called "dynamical Auger emission." The experimental results are supported by ab initio quantum chemical calculations restricted to a linear geometry of the core-excited state.
Ludwik Adamowicz - One of the best experts on this subject based on the ideXlab platform.
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Electron affinity of Li7 calculated with the inclusion of Nuclear Motion and relativistic corrections
The Journal of chemical physics, 2007Co-Authors: Monika Stanke, Dariusz Kȩdziera, Sergiy Bubin, Ludwik AdamowiczAbstract:Explicitly correlated Gaussian functions have been used to perform very accurate variational calculations for the ground states of Li7 and Li−7. The Nuclear Motion has been explicitly included in the calculations (i.e., they have been done without assuming the Born-Oppenheimer (BO) approximation). An approach based on the analytical energy gradient calculated with respect to the Gaussian exponential parameters was employed. This led to a noticeable improvement of the previously determined variational upper bound to the nonrelativistic energy of Li−. The Li energy obtained in the calculations matches those of the most accurate results obtained with Hylleraas functions. The finite-mass (non-BO) wave functions were used to calculate the α2 relativistic corrections (α=1∕c). With those corrections and the α3 and α4 corrections taken from Pachucki and Komasa [J. Chem. Phys. 125, 204304 (2006)], the electron affinity (EA) of Li7 was determined. It agrees very well with the most recent experimental EA.
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Ionization potential of Be9 calculated including Nuclear Motion and relativistic corrections
Physical Review A, 2007Co-Authors: Monika Stanke, Dariusz Kȩdziera, Sergiy Bubin, Ludwik AdamowiczAbstract:Variational calculations employing explicitly correlated Gaussian functions have been performed for the ground states of {sup 9}Be and {sup 9}Be{sup +} including the Nuclear Motion [i.e., without assuming the Born-Oppenheimer (BO) approximation]. An approach based on the analytical energy gradient calculated with respect to the Gaussian exponential parameters was employed, leading to energies of the two systems noticeably improved over those found in the recent paper of Pachucki and Komasa [Phys. Rev. A 73, 052502 (2006)]. The non-BO wave functions were used to calculate the {alpha}{sup 2} relativistic corrections ({alpha}=e{sup 2}/({Dirac_h}/2{pi})c). With those corrections and the {alpha}{sup 3} and {alpha}{sup 4} corrections taken from Pachucki and Komasa, a new value of the ionization potential (IP) of {sup 9}Be was determined. It agrees very well with the most recent experimental IP.
