Séminaires de Physique Moléculaire


Séminaire DPM : Matthieu Génévriez « Experimental studies of the photodetachment of negative ions »

Intervenant : Matthieu Génévriez

Diplômé 2012 du Master de Physique de l’Université de Rennes 1, vient de compléter sa thèse àl’Institute of Condensed Matter and Nanosciences, Université Catholique de Louvain, Belgique. Il présentera des résultats de sa thèse.

DATE : le jeudi 19 octobre à 16h, salle 50 au bâtiment 11B

Résumé :
Negative ions are weakly bound systems in which electron correlations
play a predominant role. Photodetachment, i.e., the photoelectric effect
for anions, is a convenient way to probe these fragile ions, which
possess only a few bound states. Beyond its interest for the basic study
of few-body, strongly correlated systems, photodetachment is also an
important phenomenon for stellar and atmospheric physics, a major
example being the fact that photodetachment of H- is responsible for
most of the Sun’s opacity in the visible and near-infrared parts of the
electromagnetic spectrum. In view of this importance, recent alleged
discrepancies between theory and experiment have prompted new studies of
the photodetachment atomic anions.

The seminar will be dedicated to results we have recently obtained on
the photodetachment of the hydrogen, helium and oxygen atomic anions.
Early work was devoted to measuring absolute one- and two-photon
photodetachment cross sections using a new, robust technique developed
in-house. Measurements were performed over unprecedented photon energy
ranges, and helped to resolve persistent discrepancies between theory
and experiment. We have also constructed a velocity map imaging
spectrometer with the aim of recording the 3-dimensional velocity
distribution of the photodetached electrons, and have used it in a
series of measurements on O-. Finally, results on the strong-field,
sequential double photodetachment of He- will be presented, with
emphasis on how the combination of theory and experiment provides a
detailed understanding of the intricate series of resonances at play.

Publié dans Physique Moléculaire, Séminaires de Physique Moléculaire | Commentaires fermés sur Séminaire DPM : Matthieu Génévriez « Experimental studies of the photodetachment of negative ions »

Séminaire Ilsa Cooke : « Diffusion, Desorption & Destruction: Energetic and Thermal Processing of Interstellar Ices »

Intervenante : Ilsa Cooke (Department of Chemistry, University of Virginia, USA)

Date et lieu :  jeudi 5 octobre 14h-15h dans la salle 50 B11B

The interstellar medium, despite its chemically hostile environment, is host to a rich chemistry including several large organic molecules. Many of these species originate from reactions in icy dust grain mantles and are subsequently transferred to the gas, either by warm-up during star formation or by non-thermal mechanisms. The influence of these icy dust grains extends to protoplanetary disks, in which they play an important role in the rate of formation and composition of planetary systems. A large amount of work has been produced in the past few decades to study analogues of astrophysical ice mantles; however, many of the processes occurring within the ices remain to be quantified. Astrochemical models have historically focused on gas phase chemistry, though increasingly sophisticated surface chemistry models are now being implemented. These models rely on accurate rates, cross sections and barriers for processes at the surface and in the bulk of ice mantles. In this talk, I will present quantitative laboratory measurements of diffusion, desorption and destruction processes in interstellar ice analogues. In part one, I will describe CO2 ice spectroscopy focusing on CO2 longitudinal phonons as a tool to study ice mixing and diffusion. In parts two and three, I will discuss our measurements of diffusion and desorption barriers for CO:CO2 binary ices. Lastly, I will present our current work to produce a new body of photodestruction cross sections for a range of astrophysically-relevant ice species. Each of these studies provides quantitative data that can be directly input into astrochemical models and that will be particularly important as we learn more about interstellar ice composition with JWST.

Publié dans Départements, Physique Moléculaire, Séminaires de Physique Moléculaire | Commentaires fermés sur Séminaire Ilsa Cooke : « Diffusion, Desorption & Destruction: Energetic and Thermal Processing of Interstellar Ices »

Séminaire Etienne Mangaud : « Quantum dynamics of electron transfer in strongly coupled environments »

DATE : 13 juin 2017 à 10h00 en salle 120

Etienne MANGAUD,  Laboratoire de Chimie Physique, UMR8000, Université Paris-Sud, ORSAY

Experiments of time-resolved bidimensional spectroscopy carried out in complex
systems, such as photosynthetic systems (FMO)[1] or conjugated polymers[2], showed that quantum coherences amongst electronic excited states can persist for long times, comparable to the electron or excitation energy transfer times.
In order to investigate these phenomena from a theoretical point of view, one needs to
study the quantum motion of the nuclei and its influence onto the transfer. In the systems at stake, photo-induced electron transfer are studied in an oligothiophene-fullerene heterojunction[3] and a chromoprotein cryptochrome[4] as shown on Fig. 1 with a realistic environment.

Figure 1 Photo-induced electron transfer systems under study: On the left (Panel (a)), oligothiophene (OT4) –fullerene (C60) heterojunction. On the right (Panel (b)), chromoprotein cryptochrome with a flavin-adenosin-diphosphate (FAD) chromophore and a chain of three tryptophan molecules (W400, W377 and
W324)
For the heterojunction (Fig. 1 (a)), a reference Hamiltonian[5] describing a
donor-acceptor electronic system coupled to a bath of harmonic oscillators has been used. For the cryptochrome (Fig. 1 (b)), a three electronic states Hamiltonian has been parameterized using QM/MM trajectories based on constrained DFT (cDFT).[6,7]
Based on these parametrized Hamiltonians, time propagations have been carried out
using methods of dissipative quantum dynamics. However, since these systems exhibit a strong system-bath coupling that cannot be handled with traditional perturbation theory, one has to resort to exact computations such as the hierarchical equation of motion method.[8] A special care has also been taken to evaluate the quantum memory effects which prove to be significant in these systems.[9] To catch a glimpse of the physical movement at stake in the transfer, we perform a coordinate transformation used to define an effective mode[10], which is included into
the system, and which itself is coupled to a secondary bath. S H H 4 (a) (b)

As main results, we show and explain the dynamical behavior of various cases leading to an easy delocalization or to a trapping of the charge and assess the time scales of the transfer.
In the cases considered, the proposed methodology is well suited to analyze the subtle interplay between charge transfer and nuclear deformations, a prototype situation for many important processes in chemical and biological systems.
Acknowledgement: We acknowledge I. Burghardt for providing the heterojunction Hamiltonian data and F. Cailliez for fruitful discussions.

References:
[1] G. S. Engel et al, Nature, 2007, 446, 78
[2] E. Collini and G. Scholes, Science, 2009, 323, 369
[3] A. Chenel, E. Mangaud, I. Burghardt, C. Meier, M. Desouter-Lecomte, J. Chem. Phys., 2014, 140, 044104
[4] T. Firmino, E. Mangaud, F. Cailliez, A. Devolder, D. Mendive-Tapia, F. Gatti, C. Meier, M. Desouter-Lecomte, A. de la Lande, Phys. Chem. Chem. Phys., 2016, 18, 21442
[5] H. Tamura, I. Burghardt, and M. Tsukada, J. Phys. Chem. C, 2011, 115, 10205
[6] J. Řezáč, B. Lévy, I. Demachy, A. de la Lande, J. Chem. Theory Comput., 2012, 8,418
[7] Q. Wu, T. Van Voorhis, J. Chem. Theory Comput., 2006, 2,765
[8] Y. Tanimura, R. Kubo, J. Phys. Soc. Jpn., 1989, 58, 101
[9] H.-P. Breuer, E.M. Laine, J. Piilo and B. Vacchini, Rev. Mod. Phys., 2016, 88, 021003
[10] A. Pereverzev, E. R. Bittner, I. Burghardt, J. Chem. Phys., 1999, 131, 034104

Publié dans Physique Moléculaire, Séminaires de Physique Moléculaire | Commentaires fermés sur Séminaire Etienne Mangaud : « Quantum dynamics of electron transfer in strongly coupled environments »

Séminaire DPM : Philippe BODUCH « Des ions lourds et des glaces pour l’astrophysique »

DATE :27 AVRIL 2017 – 10H00 – Salle 050 , Bât 11B

INTERVENANT : Philippe BODUCH
Université de Caen Normandie – CIMAP/GANIL

Depuis 2008, une équipe du CIMAP-GANIL se concentre sur l’irradiation de glaces d’intérêt astrophysique avec des ions lourds. Ces glaces sont composées de molécules simples telles que H2O, CO, CO2, NH3… Elles sont présentes sur les comètes, les satellites de certaines planètes (lunes joviennes par ex.) et sur les grains composant les nuages denses. Ces glaces sont soumises à différentes radiations présentes dans l’espace : UV, vents stellaires, rayons cosmiques… Les irradiations aux protons et aux UV ont fait l’objet de nombreuses études. Avec les ions lourds, seules quelques études ont été réalisées à basse énergie. Il nous a donc paru important de simuler en laboratoire les interactions entre des ions lourds rapides et les glaces présentes dans l’espace afin de comprendre le rôle des rayons cosmiques dans l’évolution de ces glaces. Ces ions déposent localement une très grande quantité d’énergie. Ils peuvent alors générer des effets non observables avec des particules plus légères. Dans ce cadre, je présenterai l’étude de glaces simples et des mélanges à une température de 15 K irradiées par des ions lourds produits par le GANIL (Grand Accélérateur National d’Ions Lourds, Caen, France). Les effets d’irradiations sont analysés in situ par spectroscopie photonique (infra-rouge par transformée de Fourier et UV-Visible). Les résultats présentés lors de ce séminaire porteront sur les effets induits sur la structure de la glace, sur les modifications chimiques et sur le rôle de l’implantation. Les perspectives seront aussi abordées, notamment sur l’utilisation d’un nouveau dispositif ultravide IGLIAS financé par l’ANR ainsi que les travaux sur les molécules plus complexes (molécules aromatiques hétérocycliques, par ex.).

Publié dans Départements, Physique Moléculaire, Séminaires de Physique Moléculaire | Commentaires fermés sur Séminaire DPM : Philippe BODUCH « Des ions lourds et des glaces pour l’astrophysique »

Séminaire DPM: David Wilkowski « Ultracold strontium gas from light transport to simulators and prospect in ultracold molecules »

DATE :  jeudi 20 avril, 10h, salle 120 bât. 11E

David Wilkowski – Associate professor
Nanyang Technological University, Singapore
UMI 3654 Majulab, Centre for Quantum Technologies (CQT/NUS), Physics and Applied Physics (SPMS/NTU), Centre for Disruptive Photonic Technologies (CDPT/NTU).

 I will present some recent experiments, done on an ultracold gas of strontium atom. In particular, we studied the coherent light transport in the cold atomic ensemble. Here, the latter can be view as a random scattering medium. When the system is excited by a resonant laser beam, cooperative emission occurs in the forward direction which has characteristic time much faster that the single atom emission decay time. This phenomena show interesting similarity with Dicke superradiance.

I will also give two examples of how we use our ultracold atom system as a simulator of complex (interacting) system. The first example concerns the simulation of statistical ensemble subject to long-range  gravitational-like interaction. An interesting situation occurs for two-dimensional systems where a phase transition brings the gas into a collapse phase. A second example is the generation of an effective non-Abelian gauge field which can be view as a generalisation of the Berry phase in systems having SU(2) symmetry.

Finally I will discuss prospect of laser cooling of simple molecules and what new physics can be targeted in contrast to atomic system.

Publié dans Départements, Physique Moléculaire, Séminaires de Physique Moléculaire | Commentaires fermés sur Séminaire DPM: David Wilkowski « Ultracold strontium gas from light transport to simulators and prospect in ultracold molecules »

Séminaire Piergiorgio Casavecchia : Space-time distribution of reaction products / Unraveling the molecular mechanism of elementary chemical reactions

Intervenant : Professeur Piergiorgio Casavecchia (Université de Perugia, Italie)

DATE :  jeudi 30 mars à 14h30 dans l’amphi Grandjean au bâtiment 10 B

Résumé : Measuring the space-time distribution of reaction products, as can be performed in crossed molecular beams scattering experiments, allows one to probe in detail, at the atomic/molecular level, the mechanism of elementary chemical reactions, especially when experiments are carried out in synergy with accurate theoretical calculations. Exploiting this approach, tremendous progress has been made over the past 20 years in our understanding of simple, one-channel, direct reactions, such as H+H2 and F+H2 (and their isotopic variants). Things become more complex with polyatomic multi-channel elementary reactions, such as, for instance, those of ground-state oxygen atoms, O(3P), with unsaturated hydrocarbons which, besides being of fundamental interest, are of great relevance in combustion science. These reactions are in fact characterized by a variety of energetically open, competing radical/molecular product channels, some of which can only take place via intersystem crossing (ISC) from the triplet to the singlet potential energy surface. Since the 1950s the determination of the primary products, branching ratios and detailed dynamics of these reactions, including the role played by ISC, has represented a challenge for both experimentalists and theorists. Recently, however, much progress has been made in this area owing to advances in experimental techniques (of both reaction dynamics and kinetics) as well as theoretical methodologies (electronic structure and statistical/dynamical calculations).
This talk will highlight the powerful and invaluable role played by the crossed molecular beams scattering method with universal soft ionization mass spectrometric detection and time-of-flight analysis, backed by synergic high-level theoretical calculations, for disentangling the complex mechanism and dynamics of polyatomic, multichannel non-adiabatic reactions of O(3P) with small unsaturated hydrocarbons (alkynes, alkenes and dienes). The central role played by ISC in this class of reactions and its dependence on molecular complexity and structure will be discussed.

Publié dans Départements, Physique Moléculaire, Séminaires de Physique Moléculaire | Commentaires fermés sur Séminaire Piergiorgio Casavecchia : Space-time distribution of reaction products / Unraveling the molecular mechanism of elementary chemical reactions

Séminaire Phys. Mol. / Lucile Rutkowski : Spectroscopie par peignes de fréquences

DATE : 04 AVRIL 2017 à 14h00 en salle 120

Intervenante : Lucile Rutkowski , Department of Physics, Umeå university

Cavity-enhanced optical frequency comb spectroscopy: developments and applications.
Optical frequency combs offer unprecedented combination of spectral coverage, high resolution and high-sensitivity when combined with enhancement cavities. They enable simultaneous detection of multiple species and/or of entire molecular absorption bands, reducing the influence of the fluctuations of the experiment environment on the final result. I will present the principle of the two types of spectrometers I have contributed to develop and worked with: the Vernier continuous filtering spectrometer (during my PhD in Lyon), based on the coupling of a comb in a detuned cavity, and the comb-based Fourier transform spectrometer with sub-nominal resolution (during postdoc in Umeå, Sweden). I will show results for atmospheric detection in the visible and the mid-infrared ranges, OH and H2O detection in combustion diagnostics in the telecom near-infrared spectral range, and high precision absorption and dispersion spectroscopy of CO2 still in the telecom range.

 

Publié dans Départements, Physique Moléculaire, Séminaires de Physique Moléculaire | Commentaires fermés sur Séminaire Phys. Mol. / Lucile Rutkowski : Spectroscopie par peignes de fréquences

Thomas Bourdel : « Diffusion non-linéaire d’un soliton brillant atomique en présence de désordre »

  • vendredi 16 décembre 2016 à 16h00
  • salle 50

Résumé :

Dans la nature, le désordre joue souvent un rôle important dans la propagation des ondes ou des particules. En l’absence d’interaction, les phénomènes de diffusion ou même de localisation de Anderson dû à la cohérence des ondes sont bien connus et globalement compris. Il y a cependant de nombreuses situations pour lesquelles les interactions jouent un rôle important, par exemple pour les électrons en matière condensée ou pour la lumière dès qu’il y a de l’effet Kerr. La compréhension des effets conjoints du désordre et des interactions reste ainsi un défi important.

Nous étudions expérimentalement ce problème dans le cas particulier d’un soliton brillant d’onde de matière, c’est à-dire un condensat de Bose-Einstein unidimensionnel qui en l’absence de désordre se propage sans dispersion grâce à des interactions attractives. Le désordre est ajouté de façon contrôlée grâce à un speckle optique. Dans le cas où l’énergie d’interaction entre atomes est de l’ordre de leur énergie cinétique, les atomes ont tendance à être collectivement soit réfléchis, soit transmis. Nous observons donc un comportement non linéaire de la diffusion. Nos résultats sont reproduits dans une approche de champ moyen de type équation de Schrödinger non-linéaire. Pour des nombres petits d’atomes, on s’attend au contraire à une superposition cohérente d’un soliton à la fois réfléchi et transmis, un état qui pourrait permettre une interférométrie au delà de la limite quantique standard.

Thomas Bourdel : Laboratoire Charles-Fabry, Institut d’Optique

Publié dans Physique Moléculaire, Séminaires de Physique Moléculaire | Commentaires fermés sur Thomas Bourdel : « Diffusion non-linéaire d’un soliton brillant atomique en présence de désordre »

séminaire DPM* : David CARTY « Monitoring Breath Acetone in Real Time in Diabetics »

DATE :  13/10/2016 10h30-11h30 B11E salle 120

Intervenant : David CARTY
Departments of Chemistry and Physics
University of Durham
United Kingdom

Type-I diabetes mellitus (T1D) is a degenerative metabolic condition whereby insulin producing cells in the pancreas die off. Ultimately, this leads to a complete inability to produce insulin, which is vital to be able to metabolise glucose for energy. The peak age at which T1D begins is 14. Very many children at the onset of T1D are not diagnosed with T1D until they are seriously ill with a condition called diabetic ketoacidosis (DKA), which is a fast acting medical emergency. DKA can be fatal if not treated in time and is caused by the acidification of the blood due a build up of poisonous ketones in the bloodstream. The ketones are produced as a result of fat metabolism for energy in the absence of glucose metabolism. The treatment of DKA centres around insulin replacement and fluid replacement, as sufferers are are also usually severely dehydrated, with the hope that the DKA is resolved gradually over a 12 to 18 hour period. However, while ketones and blood pH can be measured straightforwardly in a blood sample, regular sampling of blood is invasive, often distressing for young patients and the results are not received by clinicians quickly enough to influence changes in treatment.

In Durham, we are in the early stages of developing a non-invasive, real time, quantitative bedside sensor/monitor for ketones for the treatment of DKA in hospitals in the hope that timely feedback on a patient’s condition will enable better personalised treatment with improved outcomes. The device targets acetone that is present in the breath of patients and absolute concentration measurements are made using a technique of our invention called cavity-enhanced laser induced fluorescence (CELIF). In this talk, I will discuss why there is an unmet clinical need for such a monitor. I will discuss how CELIF works, the performance specifications such a device must have and I will show you the progress we have made.

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*Ce séminaire sera intégré au « Cycle de Séminaires de Physique » destiné aux doctorants et validé par l’Ecole Doctorale SDLM 

Publié dans Départements, Physique Moléculaire, Séminaires de Physique Moléculaire | Commentaires fermés sur séminaire DPM* : David CARTY « Monitoring Breath Acetone in Real Time in Diabetics »

Séminaire DPM* : Mitchio Okumura, « Synchrotron Photoionization Mass Spectrometry Studies of Atmospheric Free Radical Kinetics and Spectroscopy »

DATE :mercredi 21/09/2016 11h00-12h00 B11E salle 120

Intervenant : Mitchio Okumura,  Professor of Chemical Physics California Institute of Technology Division of Chemistry & Chemical Engineering Arthur Amos Noyes Laboratory, MS 127‑72 Pasadena, CA 91125 USA

*Ce séminaire sera intégré au « Cycle de Séminaires de Physique » destiné aux doctorants et validé par l’Ecole Doctorale SDLM


							
Publié dans Départements, Physique Moléculaire, Séminaires de Physique Moléculaire | Commentaires fermés sur Séminaire DPM* : Mitchio Okumura, « Synchrotron Photoionization Mass Spectrometry Studies of Atmospheric Free Radical Kinetics and Spectroscopy »