Peer-reviewed Publications |
Awali, S., Mestdagh, J. - M., Gaveau, M. - A., Briant, M., Soep, B., Mazet, V., & Poisson, L. (2021). Time-Resolved Observation of the Solvation Dynamics of a Rydberg Excited Molecule Deposited on an Argon Cluster. II. DABCO* at Long Time Delays. J Phys Chem A, 125(20), 4341–4351.
Résumé: The real-time dynamics of DABCO-argon clusters is investigated in a femtosecond pump-probe experiment where the pump excites DABCO to the S1 state within the argon cluster. The probe operates by photoionization and documents the energy and angular distributions of the resulting photoelectrons. The present work complements a previous work from our group [Awali Phys. Chem. Chem. Phys., 2014, 16, 516-526] where this dynamics was probed at short time, up to 4 ps after the pump pulse. Here, the dynamics is followed up to 500 ps. A multiscale dynamics is observed. It includes a jump between two solvation sites (time scale 0.27 ps) followed by the relaxation of the solvation cage excess vibrational energy (time scale 14 ps) and then by that of DABCO (time scale >150 ps). Polarization anisotropy, double polarization, and angular anisotropy effects are reported also. They are interpreted (quantitatively for the former effect) in terms of decoherence of rotational alignment, driven by the overall rotation of the DABCO-argon clusters. A tomographic view of the DABCO excited orbital, provided by the double anisotropy effect, is discussed on a qualitative basis.
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Deppner, C., Herr W, Cornelius, M., Stromberger P, Sternke T, Grzeschik, C., Grote A, Rudolph, J., Herrmann S, Krutzik, M., Wenzlawski A, Corgier R, Charron E, Guery-Odelin, D., Gaaloul N, Lammerzahl, C., Peters A, Windpassinger P, & Rasel, E. M. (2021). Collective-Mode Enhanced Matter-Wave Optics. Phys Rev Lett, (127), 100401.
Résumé: In contrast to light, matter-wave optics of quantum gases deals with interactions even in free space and for ensembles comprising millions of atoms. We exploit these interactions in a quantum degenerate gas as an adjustable lens for coherent atom optics. By combining an interaction-driven quadrupole-mode excitation of a Bose-Einstein condensate (BEC) with a magnetic lens, we form a time-domain matter-wave lens system. The focus is tuned by the strength of the lensing potential and the oscillatory phase of the quadrupole mode. By placing the focus at infinity, we lower the total internal kinetic energy of a BEC comprising 101(37) thousand atoms in three dimensions to 3/2 kB.38-7;+6 pK. Our method paves the way for free-fall experiments lasting ten or more seconds as envisioned for tests of fundamental physics and high-precision BEC interferometry, as well as opens up a new kinetic energy regime.
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Holzmeier, F., Joseph, J., Houver, J. C., Lebech, M., Dowek, D., & Lucchese, R. R. (2021). Influence of shape resonances on the angular dependence of molecular photoionization delays. Nat. Commun., .
Résumé: Characterizing time delays in molecular photoionization as a function of the ejected electron emission direction relative to the orientation of the molecule and the light polarization axis provides unprecedented insights into the attosecond dynamics induced by extreme ultraviolet or X-ray one-photon absorption, including the role of electronic correlation and continuum resonant states. Here, we report completely resolved experimental and computational angular dependence of single-photon ionization delays in NO molecules across a shape resonance, relying on synchrotron radiation and time-independent ab initio calculations. The angle-dependent time delay variations of few hundreds of attoseconds, resulting from the interference of the resonant and non-resonant contributions to the dynamics of the ejected electron, are well described using a multichannel Fano model where the time delay of the resonant component is angle-independent. Comparing these results with the same resonance computed in e-NO+ scattering highlights the connection of photoionization delays with Wigner scattering time delays. It is an interesting topic to find the time it takes for an electron to escape an atom or a molecule after photoionization. Here the authors measure the angular dependence of photoionization time delay in the molecular frame and discuss the role of shape resonances.
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Mainali, S., Gatti, F., Iouchtchenko, D., Roy, P. - N., & Meyer, H. - D. (2021). Comparison of the multi-layer multi-configuration time-dependent Hartree (ML-MCTDH) method and the density matrix renormalization group (DMRG) for ground state properties of linear rotor chains. J. Chem. Phys., 154, 174106.
Résumé: We demonstrate the applicability of the Multi-Layer Multi-Configuration Time-Dependent Hartree (ML-MCTDH) method to the problem of computing ground states of one-dimensional chains of linear rotors with dipolar interactions. Specifically, we successfully obtain energies, entanglement entropies, and orientational correlations that are in agreement with the Density Matrix Renormalization Group (DMRG), which has been previously used for this system. We find that the entropies calculated by ML-MCTDH for larger system sizes contain non-monotonicity, as expected in the vicinity of a second-order quantum phase transition between ordered and disordered rotor states. We observe that this effect remains when all couplings besides nearest-neighbor are omitted from the Hamiltonian, which suggests that it is not sensitive to the rate of decay of the interactions. In contrast to DMRG, which is tailored to the one-dimensional case, ML-MCTDH (as implemented in the Heidelberg MCTDH package) requires more computational time and memory, although the requirements are still within reach of commodity hardware. The numerical convergence and computational demand of two practical implementations of ML-MCTDH and DMRG are presented in detail for various combinations of system parameters.
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Voute A, Gatti F, Moller KB, & Henriksen NE. (2021). Femtochemistry of bimolecular reactions from weakly bound complexes: computational study of the H + H'OD --> H'OH + D or HOD + H' exchange reactions. Phys Chem Chem Phys, (23), 27207–27226.
Résumé: A full-dimensional wavepacket propagation describing the bimolecular exchange reactions H + H'OD --> H'OH + D or HOD + H' initiated by photolysis of HCl in the hydrogen-bound complex (HCl)---(HOD) is reported. The dynamics of this reaction is carried out with the MCTDH method on an ab initio potential energy surface (PES) of H3O and the initial state is derived from the ground state wavefunction of the complex obtained by relaxation on its own electronic ground state ab initio PES. The description of the system makes use of polyspherical coordinates parametrizing a set of Radau and Jacobi vectors. The calculated energy- and time-resolved reaction probabilities show, owing to the large collision energies at play stemming from the (almost full) photolysis of HCl, that the repulsion between oxygen in the H'OD molecule and the incoming hydrogen atom is the main feature of the collision and leads to non-reactive scattering. No abstraction reaction products are observed. However, both exchange processes are still observable, with a preference in O-H' bond dissociation over that of O-D. The selectivity is reversed upon vibrational pre-excitation of the O-D stretching mode in the H'OD molecule. It is shown that, after the collision, the hydrogen atom of HCl does most likely not encounter the almost stationary chlorine atom again but we also consider the limit case where the H atom is forced to collide multiple times against H'OD as a result of being pushed back by the Cl atom.
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Zhang X, Zhang, Z., Gatti, F., & Zhang, D. H. (2021). Full-dimensional quantum dynamics study of isotope effects for the H2 + NH2/ND2/NHD and H2/D2/HD + NH2 reactions. J Chem Phys, 154, 074301.
Résumé: A full-dimensional quantum dynamical study for the bimolecular reactions of hydrogen molecules with amino radicals for different isotopologues is reported. The nonreactive amino radical is described by two Radau vectors that are very close to the valence bond coordinates. Potential-optimized discrete variable representation basis is used for the vibrational coordinates of the amino radical. Starting from the reaction H2 + NH2, we study the isotope effects for the two reagents separately, i.e., H2 + NH2/ND2/NHD and H2/D2/HD + NH2. The effects of different vibrational mode excitations of the reagents on the reactivities are studied. Physical explanations about the isotope effects are also provided thoroughly including the influence of vibrational energy differences between the different isotopologues and the impact of the tunneling effect.
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