Magazine Articles |
|
Bourguignon, B., Béroff, K., Bréchignac, P., Dujardin, G., Leach, S., & and Zehnacker-Rentien, A. (2017). In the wake of Physical Chemistry under irradiation: onward to the Institute of Molecular Sciences at Orsay. Histoire de la Recherche Contemporaine, 6, 16–27.
|
|
Peer-reviewed Publications |
Babilotte, P., Coudert, L. H., Billard, F., Hertz, E., Faucher, O., & Lavorel, B. (2017). Experimental and theoretical study of free induction decay of water molecules induced by terahertz laser pulses. PRA, 95(4), 043408.
Résumé: We experimentally investigate the free induction decay in the asymmetric top molecule H2O after interaction with short terahertz pulses. Two different experimental techniques are used to perform measurements in the gas phase under different experimental conditions: electro-optical detection and terahertz field-induced second-harmonic generation. Simulations of the free induction decay signals are performed with a theoretical approach in which the absorption and dispersion coefficients are evaluated from spectroscopic data pertaining to the water molecule. Experimental and theoretical signals are compared directly in the time domain in two limiting cases. For a short propagation length of ∼40 cm, both signals show a slightly altered electric field consistent with the approximation of weak absorption and dispersion. For a longer propagation length of ∼300 cm, the electric field is heavily distorted. A good agreement between experimental and calculated signals is obtained in both cases. Finally, we discuss the advantages and/or disadvantages of the two experimental techniques.
|
|
|
Carlos, M., Gruson, O., Richard, C., Boudon, V., Rotger, M., Thomas, X., Maul, C., Sydow, C., Domanskaya, A., Georges, R., Soulard, P., Pirali, O., Goubet, M., Asselin, P., & Huet, T. R. (2017). High-resolution spectroscopy and global analysis of CF4 rovibrational bands to model its atmospheric absorption. Journal of Quantitative Spectroscopy and Radiative Transfer, 201(Supplement C), 75–93.
|
|
Chartrand, A. M., McCormack, E. F., Jacovella, U., Holland, D. M. P., Gans, B., Tang, X., Garcia, G. A., Nahon, L., & Pratt, S. T. (2017). Photoelectron angular distributions from rotationally resolved autoionizing states of N2. The Journal of Chemical Physics, 147(22), 224303.
Résumé: The single-photon, photoelectron-photoion coincidence spectrum of N2 has been recorded at high (∼1.5 cm−1) resolution in the region between the N2+X2Σg+, v+ = 0 and 1 ionization thresholds by using a double-imaging spectrometer and intense vacuum-ultraviolet light from the Synchrotron SOLEIL. This approach provides the relative photoionization cross section, the photoelectron energy distribution, and the photoelectron angular distribution as a function of photon energy. The region of interest contains autoionizing valence states, vibrationally autoionizing Rydberg states converging to vibrationally excited levels of the N2+X2Σg+ ground state, and electronically autoionizing states converging to the N2+A2Π and B 2Σu+ states. The wavelength resolution is sufficient to resolve rotational structure in the autoionizing states, but the electron energy resolution is insufficient to resolve rotational structure in the photoion spectrum. A simplified approach based on multichannel quantum defect theory is used to predict the photoelectron angular distribution parameters, β, and the results are in reasonably good agreement with experiment.
|
|
Coudert, L. H. (2017). Optimal orientation of an asymmetric top molecule with terahertz pulses. The Journal of Chemical Physics, 146(2), 024303.
Résumé: Terahertz pulses effects are investigated in an asymmetric top C2v molecule using numerical simulations. The average value of the direction cosine ΦZxΦZx is computed solving the time dependent Schrödinger equation for several types of pulses. The H2S molecule taken as a test case is first subject to two short terahertz pulses with a duration smaller than 5 ps, an identical maximum value of the electric field of 2 MV/cm, but a different shape. The thermal average ⟨⟨ΦZx⟩⟩⟨⟨ΦZx⟩⟩ is calculated for several temperatures, and non-periodic time variations are found even for the lowest temperature. For a given temperature, the maximum orientation achieved is shown to be dependent on the overlap between the absorption spectrum of the molecule and the Fourier transform of the pulse. The maximum orientation is also shown to be closely related to the molecular energy increase. In a second step, the optimal control theory is used to build a 14 ps long few-cycle pulse with the same maximum value of the electric field allowing us to reach a large maximum value of ⟨ΦZx⟩⟨ΦZx⟩ equal to 0.93. A fairly good understanding of the wavefunction describing the molecule after the pulse was achieved.
|
|
Dartois, E., Chabot, M., Pino, T., Béroff, K., Godard, M., Severin, D., Bender, M., & Trautmann, C. (2017). Swift heavy ion irradiation of interstellar dust analogues. A&A, 599, A130.
Résumé: Context. Interstellar dust grain particles are immersed in vacuum ultraviolet (VUV) and cosmic ray radiation environments influencing their physicochemical composition. Owing to the energetic ionizing interactions, carbonaceous dust particles release fragments that have direct impact on the gas phase chemistry.
Aims. The exposure of carbonaceous dust analogues to cosmic rays is simulated in the laboratory by irradiating films of hydrogenated amorphous carbon interstellar analogues with energetic ions. New species formed and released into the gas phase are explored.
Methods. Thin carbonaceous interstellar dust analogues were irradiated with gold (950 MeV), xenon (630 MeV), and carbon (43 MeV) ions at the GSI UNILAC accelerator. The evolution of the dust analogues is monitored in situ as a function of fluence at 40, 100, and 300 K. Effects on the solid phase are studied by means of infrared spectroscopy complemented by simultaneously recording mass spectrometry of species released into the gas phase.
Results. Specific species produced and released under the ion beam are analyzed. Cross sections derived from ion-solid interaction processes are implemented in an astrophysical context.
|
|
Dartois, E., Jallat, A., Alata, I., Gavilan, L., Cruz-Diaz, G. A., Chabot, M., Beroff, K., & Muñoz Caro, G. M. (2017). UV Photolysis of Hydrogenated Amorphous Carbons of Astrophysical Interest. Polycyclic Aromatic Compounds, 37(2-3), 94–100.
Résumé: TIn the gas phase, most of the ionized or neutral molecules detected in the interstellar and circumstellar media contain at least one carbon atom. Carbon chemistry plays thus a dominant role in the understanding of the structure and evolution of the interstellar medium (ISM). One particular zone of interest to observe small carbonaceous radicals and molecules, are the sharp molecular clouds edges exposed to energetic photons. These photon-dominated regions are rich in these hydrocarbons (like CCH, c-C3H2, C4H), and provide tests for the chemistry models in the diffuse to molecular transition. The pure gas phase models generally fail in reproducing the abundance of many of the observed species, and several authors suggest such abundances may arise from the products of the VUV photodissociation of carbonaceous grains or PAHs. Hydrogenated amorphous carbons (a-C:H or HAC), abundantly observed in the ISM, could also be at the origin of many of these small carbonaceous radicals. Experimentally, this work investigates the production and release of hydrocarbons from the VUV photolysis of a-C:H interstellar analogues under ultra-high vacuum. The experimental results are applied to a Photon Dominated Region model to constrain the impact of this release on the observed gas phase species.
|
|
Demaison, J., Craig, N. C., Gurusinghe, R., Tubergen, M. J., Rudolph, H. D., Coudert, L. H., Szalay, P. G., & Császár, A. G. (2017). Fourier Transform Microwave Spectrum of Propene-3-d1 (CH2═CHCH2D), Quadrupole Coupling Constants of Deuterium, and a Semiexperimental Equilibrium Structure of Propene. The Journal of Physical Chemistry A, 121(16), 3155–3166.
Résumé: The ground-state rotational spectrum of propene-3-d1, CH2═CHCH2D, was measured by Fourier transform microwave spectroscopy. Transitions were assigned for the two conformers, one with the D atom in the symmetry plane (S) and the other with the D atom out of the plane (A). The energy difference between the two conformers was calculated to be 6.5 cm–1, the S conformer having lower energy. The quadrupole hyperfine structure due to deuterium was resolved and analyzed for both conformers. The experimental quadrupole coupling and the centrifugal distortion constants compared favorably to their ab initio counterparts. Ground-state rotational constants for the S conformer are 40582.157(9), 9067.024(1), and 7766.0165(12) MHz. Ground-state rotational constants for the A conformer are 43403.75(3), 8658.961(2), and 7718.247(2) MHz. For the A conformer, a small tunneling splitting (19 MHz) due to internal rotation was observed and analyzed. Using the new rotational constants of this work as well as those previously determined for the 13C species and for some deuterium-substituted species from the literature, a new semiexperimental equilibrium structure was determined and its high accuracy was confirmed. The difficulty in obtaining accurate coordinates for the out-of-plane hydrogen atom is discussed.
|
|
Gans, B., Boyé-Péronne, S., Garcia, G. A., Roeder, A., Schleier, D., Halvick, P., & Loison, J. - C. (2017). Unveiling the ionization energy of the CN radical. J. Phys. Chem. Lett., 8, 4038–4042.
Résumé: The cyano radical is an ubiquitous molecule, and was for instance one of the first species detected in astrophysical media such as comets or diffuse clouds. In photodis- sociation regions the reaction rate of CN+ + CO → CN + CO+ is one of the critical parameters defining nitrile chemistry. The enthalpy of this charge transfer reaction is defined as the difference of ionization energies (EI) between CN and CO. Although EI(CO) is known accurately, the EI(CN) values are more dispersed and deduced indirectly from thermodynamic thresholds only, all above EI(CO), leading to the assumption that the reaction was fast even at low temperature. Using a combination of synchrotron radiation, electron/ion imaging coincidence techniques, and supporting ab initio calculations, we directly determine the first adiabatic ionization energy of CN at 13.956(7) eV, and we demonstrate that EI(CO) > EI(CN). The findings suggest a very slow reaction in the cold regions of interstellar media.
|
|
Gans, B., Garcia, G. A., Holzmeier, F., Krüger, J., Röder, A., Lopes, A., Fittschen, C., Loison, J. - C., & Alcaraz, C. (2017). Communication: On the first ionization threshold of the C2H radical. The Journal of Chemical Physics, 146(1), 011101.
Résumé: The slow photoelectron spectrum of the ethynyl radical has been recorded for the first time by using the DESIRS beamline of the SOLEIL synchrotron facility. Ethynyl was generated using a microwave discharge flow tube. The observation of the X+Π3←XΣ+2Π3←XΣ+2 transition allowed the first direct measurement of the adiabatic ionization threshold of this radical (EI = 11.641(5) eV). The experimental results are supported by ab initio calculations. Our preliminary investigation of the cationic ground state potential energy surfaces predicts a non-negligible Renner-Teller effect which has not been discussed previously.
|
|
Garcia, G. A., Krüger, J., Gans, B., Falvo, C., Coudert, L. H., & and Loison, J. C. (2017). Valence shell threshold photoelectron spectroscopy of the CHxCN (x = 0-2) and CNC radicals. The Journal of Chemical Physics, 147(1), 013908.
Résumé: We present the photoelectron spectroscopy of four radical species, CHxCN (x = 0-2) and CNC, formed in a microwave discharge flow-tube reactor by consecutive H abstractions from CH3CN (CHxCN + F → CHx−1CN + HF (x = 1-3)). The spectra were obtained combining tunable vacuum ultraviolet synchrotron radiation with double imaging electron/ion coincidence techniques, which yielded mass-selected threshold photoelectron spectra. The results obtained for H2CCN complement existing ones while for the other radicals the data represent the first observation of their (single-photon) ionizing transitions. In the case of H2CCN, Franck-Condon calculations have been performed in order to assign the vibrational structure of the X+ 1A1←X 2B1 ionizing transition. A similar treatment for the HCCN, CCN, and CNC radicals appeared to be more complicated mainly because a Renner-Teller effect strongly affects the vibrational levels of the ground electronic state of the HCCN+, CCN, and CNC species. Nevertheless, the first adiabatic ionization energies of these radicals are reported and compared to our ab initio calculated values, leading to new values for enthalpies of formation (ΔfH0298(HCCN+(X2A′))=1517±12kJmol−1,ΔfH298(CCN(X2Π))=682±13kJmol−1(ΔfH298(HCCN+(X2A′)=1517±12kJmol−1,ΔfH298(CCN(X2Π))=682±13kJmol−1, and ΔfH298(CNC(X2Πg))=676±12kJmol−1)ΔfH298(CNC(X2Πg))=676±12kJmol−1), which are of fundamental importance for astrochemistry.
|
|
Gavilan, L., Le, K. C., Pino, T., Alata, I., Giuliani, A., & Dartois, E. (2017). Polyaromatic disordered carbon grains as carriers of the UV bump: Far-UV to mid-IR spectroscopy of laboratory analogs. A&A, 607, A73.
Résumé: Context. A multiwavelength study of laboratory carbons with varying degrees of hydrogenation and sp2 hybridization is required to characterize the structure of the carbonaceous carriers of interstellar and circumstellar extinction.
Aims. We study the spectral properties of carbonaceous dust analogs from the far-ultraviolet to the mid-infrared and correlate features in both spectral ranges to the aromatic/aliphatic degree.
Methods. Analogs to carbonaceous interstellar dust encountered in various phases of the interstellar medium have been prepared in the laboratory. These are amorphous hydrogenated carbons (a-C:H), analogs to the diffuse interstellar medium component, and soot particles, analogs to the polyaromatic component. Thin films (d < 100 nm) have been measured in transmission in the vacuum-ultraviolet (VUV; 120–210 nm) within the atmospheric pressure experiment (APEX) chamber of the DISCO beam line at the SOLEIL synchrotron radiation facility. Spectra of these films were further measured through the UV-Vis (210 nm–1 μm) and in the mid-infrared (3–15 μm).
Results. Tauc optical gaps, Eg, are derived from the visible spectra. The major spectral features are fitted through the VUV to the mid-infrared to obtain positions, full-widths at half maximum (FWHM), and integrated intensities. These are plotted against the position of the π-π∗ electronic transitions peak. Unidentified or overlapping features in the UV are identified by correlations with complementary infrared data. A correlation between the optical gap and position of the π-π∗ electronic transitions peak is found. The latter is also correlated to the position of the sp3 carbon defect band at ~8 μm, the aromatic C=C stretching mode position at ~6 μm, and the H/C ratio.
Conclusions. Ultraviolet and infrared spectroscopy of structurally diverse carbon samples are used to constrain the nanostructural properties of carbon carriers of both circumstellar and interstellar extinction, such as the associated coherent lengths and the size of polyaromatic units. Our study suggests that carriers of the interstellar UV bump should exhibit infrared bands akin to the A/B classes of the aromatic infrared bands, while the circumstellar bump carriers should exhibit bands corresponding to the B/C classes.
|
|
|
Georges, R., Michaut, X., Moudens, A., Goubet, M., Pirali, O., Soulard, P., Asselin, P., Huet, T., Roy, P., Fournier, M., & Vigasin, A. (2017). Nuclear Spin Symmetry Conservation in 1H216O Investigated by Direct Absorption FTIR Spectroscopy of Water Vapor Cooled Down in Supersonic Expansion. The Journal of Physical Chemistry A, 121(40), 7455–7468.
|
|
Hamraoui, K., Babilotte, P., Billard, F., Hertz, E., Faucher, O., Coudert, L. H., Sugny, D., & Lavorel, B. (2017). Terahertz pulse shaping through propagation in a gas of symmetric top molecules. Phys. Rev. A, 96(4), 043416.
Résumé: Symmetric top molecules of methyl iodide are irradiated with a terahertz pulse generated by a two-color plasma and shaped by a short propagation in air. Free-induction decay is emitted by the excited molecular sample and then propagates in air before detection. The experimental data show that the input terahertz (THz) pulse undergoes strong reshaping through absorption and dispersion. This leads to narrow wave packets at revival times due to the excitation of high rotational energy levels. Typically, a THz burst of duration ≃ 15−20 ps is produced periodically, with a central frequency of ≃1 THz and a width that can be as narrow as 60–80 GHz. Pulse shaping based on propagation can be useful for quantum control in molecules. We provide a theoretical description of this wave propagation based on the Maxwell-Bloch equation. The observed experimental signal is in good agreement with the numerical simulations.
|
|
Hartmann, J. - M., Boulet, C., & Toon, G. C. (2017). Collision-induced absorption by N2 near 2.16 µm: Calculations, model and consequences for atmospheric remote sensing. J. Geophys. Res. Atmos., 122, 2419–2428.
Résumé: Classical Molecular Dynamics Simulations (CMDS) are used for calculations of the Collision Induced Absorption (CIA) by pure N2 in the (2.1-2.2 µm) region of the first overtone band. They lead to reasonable (±15%) agreement with the only two laboratory measurements available, at 97 K and room temperature. Based on these experiment/theory comparisons, empirical corrections are made to the CMDS-calculated CIA of pure N2 in the 200-300 K temperature range. In addition, the contribution of N2-O2 collisions is, in the absence of any laboratory measurement, calculated and a simple semi-empirical model (the first of its kind) is built in order to predict the CIA of N2 under Earth atmosphere conditions. This is successfully validated by comparisons with ground based atmospheric transmission spectra in the 2.1-2.2 µm region.
|
|
Hartmann, J. - M., Vander Auwera, J., Boulet, C., Birot, M., Dourges, M. - A., Toupance, T., El Hamzaoui, H., Ausset, P., Carré, Y., Kocon, L., Capoen, B., & Bouazaoui, M. (2017). Infrared absorption by molecular gases to probe porous materials and comparisons with other techniques. Microporous and Mesoporous Materials, 237, 31–37.
Résumé: Infrared transmission spectra of several molecular gases inside three porous silica samples with pore sizes ranging from 7 nm to several tens of nm have been recorded with a Fourier transform spectrometer. Their analysis shows that consistent values of the percentage of open porosity and average pore size can be retrieved from these non intrusive nor destructive optical measurements. The samples have also been characterized using mercury intrusion/extrusion and the nitrogen sorption method. The results of these different probing techniques are in good agreement when the methods used are adapted to the involved pore size. This consistency demonstrates that light absorption by confined gases is a valuable porosimetry tool.
|
|
Joblin, C., Dontot, L., Garcia, G. A., Spiegelman, F., Rapacioli, M., Nahon, L., Parneix, P., Pino, T., & Bréchignac, P. (2017). Size Effect in the Ionization Energy of PAH Clusters. The Journal of Physical Chemistry Letters, 8(15), 3697–3702.
Résumé: We report the first experimental measurement of the near-threshold photoionization spectra of polycyclic aromatic hydrocarbon clusters made of pyrene C16H10 and coronene C24H12, obtained using imaging photoelectron–photoion coincidence spectrometry with a VUV synchrotron beamline. The experimental results of the ionization energy are compared to calculated ones obtained from simulations using dedicated electronic structure treatment for large ionized molecular clusters. Experiment and theory consistently find a decrease of the ionization energy with cluster size. The inclusion of temperature effects in the simulations leads to a lowering of this energy and to quantitative agreement with the experiment. In the case of pyrene, both theory and experiment show a discontinuity in the IE trend for the hexamer. This work demonstrates the ability of the models to describe the electronic structure of PAH clusters and suggests that these species are ionized in astronomical environments where they are thought to be present.
|
|
Koshelev, M. A., Delahaye, T., Serov, E. A., Vilkov, I. N., Boulet, C., & Tretyakov, M. Y. (2017). Accurate modeling of the diagnostic 118-GHz oxygen line for remote sensing of the atmosphere. JQSRT, 196, 78–86.
Résumé: We report the results of laboratory investigations of the shape of the diagnostic atmospheric N = 1- oxygen line performed over a very wide range of pressures from 0.4 to 1000 Torr using two principally different spectrometers having complementary abilities. A spectrometer with a radio-acoustic detector of absorption was used for recording low pressure spectra spanning the 0.4–2 Torr range, and high pressure data from 250 to 1000 Torr were registered by a resonator spectrometer. The sensitivity of both instruments was improved significantly which allowed us to obtain signal-to-noise ratio at spectra recordings of the order of a few thousands. The spectra analysis enabled the first manifestation of the speed-dependence of the collision cross section of the line, along with considerable refinement of other parameters, including pressure broadening, intensity and line-mixing. The results are of primary importance for atmospheric applications.
|
|
Kumar, N., Pham-Xuan, Q., Depauw, A., Hemadi, M., Ha-Duong, N. - T., Lefevre, J. - P., Ha-Thi, M. - H., & Leray, I. (2017). New sensitive and selective calixarene-based fluorescent sensors for the detection of Cs+ in an organoaqueous medium. New J. Chem., 41(15), 7162–7170.
Résumé: Herein, new fluorescent sensors based on calix[4]arene-biscrown-6 containing extended coumarin as a fluorophore were synthetized and their photophysical properties were characterized. These compounds display intense absorption and emission spectra in the visible region due to extension of the coumarin system. Moreover, complexation properties of these ligands were reported, and the Calix-COU-Benz-CN ligand was able to selectively detect cesium ions in an organoaqueous solvent. Upon the addition of cesium, a blue-shift in the absorption spectra and an enhancement of the emission spectra were observed. This ligand was incorporated in a microfluidic device for the detection of Cs+ ions, and a detection limit of 1.4 [small mu ]M was achieved for these ions.
|
|
|
Kutzer, P., Hartung, S., Pirali, O., Pietschnig, R., Medcraft, C., Yamada, K. M. T., & Giesen, T. F. (2017). Tert-butyl-dibromophosphane tBuPBr2—a new chemical synthesis and first spectroscopic characterization. Heteroatom Chem, 28(2), e21361-n/a.
|
|
|
Launoy, T., Béroff, K., Chabot, M., Martinet, G., Le Padellec, A., Pino, T., Bouneau, S., Vaeck, N., Liévin, J., Féraud, G., Loreau, J., & Mahajan, T. (2017). Ion-pair dissociation of highly excited carbon clusters: Size and charge effects. Pra, 95(2), 022711.
|
|
Le, K. C., Lefumeux, C., & Pino, T. (2017). Differential Raman backscattering cross sections of black carbon nanoparticles. Scientific Reports, 7(1), 17124.
Résumé: We report the measurements of the differential Raman backscattering cross sections for several carbonaceous ultrafine particles of environmental relevances. These were obtained by dispersing the target particles in liquid water which was used as the internal standard reference. The optical collection was performed in a configuration to ensure a detection as close as possible to the backward direction. These are the first cross sections on black carbon-type particles although Raman spectroscopy is widely used in Carbon science. The high values of the cross sections, few 10−28 cm2.sr−1.atom−1, reflect resonance effects that take advantages of the disordered polyaromatic structures. Because they were measured in conditions intended to mimic the aerosol phase, these measurements provide a crucial step to move toward quantitative Raman spectroscopy and enable development of dedicated teledetection of black carbon in the atmosphere and in combustion chambers.
|
|
Ma, Q., Boulet, C., & and Tipping, R. H. (2017). Relaxation matrix for symmetric tops with inversion symmetry: Line coupling and line mixing effects on NH3 lines in the . The Journal of Chemical Physics, 146(13), 134312.
Résumé: Line shape parameters including the half-widths and the off-diagonal elements of the relaxation matrix have been calculated for self-broadened NH3 lines in the perpendicular ν4 band. As in the pure rotational and the parallel ν1 bands, the small inversion splitting in this band causes a complete failure of the isolated line approximation. As a result, one has to use formalisms not relying on this approximation. However, due to differences between parallel and perpendicular bands of NH3, the applicability of the formalism used in our previous studies of the ν1 band and other parallel bands must be carefully verified. We have found that, as long as potential models only contain components with K1 = K2 = 0, whose matrix elements require the selection rule Δk = 0, the formalism is applicable for the ν4 band with some minor adjustments. Based on both theoretical considerations and results from numerical calculations, the non-diagonality of the relaxation matrices in all the ^{P}P, ^{R}P, ^{P}Q, ^{R}Q, ^{P}R, and ^{R}R branches is discussed. Theoretically calculated self-broadened half-widths are compared with measurements and the values listed in HITRAN 2012. With respect to line coupling effects, we have compared our calculated intra-doublet off-diagonal elements of the relaxation matrix with reliable measurements carried out in the PP branch where the spectral environment is favorable. The agreement is rather good since our results do well reproduce the observed k and j dependences of these elements, thus validating our formalism.
|
|
|
Ma, Q., Boulet, C., & Tipping, R. H. (2017). Vibrational dependence of line coupling and line mixing in self-broadened parallel bands of NH3. JQSRT, 203, 425–433.
|
|
Mendes Marinho, S., Ha-Thi, M. - H., Pham, V. - T., Quaranta, A., Pino, T., Lefumeux, C., Chamaillé, T., Leibl, W., & Aukauloo, A. (2017). Time-Resolved Interception of Multiple-Charge Accumulation in a Sensitizer–Acceptor Dyad. Angew. Chem. Int. Ed., 56(50), 15936–15940.
Résumé: Biomimetic models that contain elements of photosynthesis are fundamental in the development of synthetic systems that can use sunlight to produce fuel. The critical task consists of running several rounds of light-induced charge separation, which is required to accumulate enough redox equivalents at the catalytic sites for the target chemistry to occur. Long-lived first charge-separated state and distinct electronic signatures for the sequential charge accumulated species are essential features to be able to track these events on a spectroscopic ground. Herein, we use a double-excitation nanosecond pump–pump–probe experiment to interrogate two successive rounds of photo-induced electron transfer on a molecular dyad containing a naphthalene diimide (NDI) linked to a [Ru(bpy)3]2+ (bpy=bipyridine) chromophore by using a reversible electron donor. We report an unprecedented long-lived two-electron charge accumulation (t=200 μs).
|
|
|
Odintsova, T. A., Tretyakov, M. Y., Pirali, O., & Roy, P. (2017). Water vapor continuum in the range of rotational spectrum of H2O molecule: New experimental data and their comparative analysis. Journal of Quantitative Spectroscopy and Radiative Transfer, 187(Supplement C), 116–123.
|
|
Parneix, P., Gamboa, A., Falvo, C., Bonnin, M. A., Pino, T., & Calvo, F. (2017). Dehydrogenation effects on the stability of aromatic units in polycyclic aromatic hydrocarbons in the interstellar medium: A computational study at finite temperature. Molecular Astrophysics, 7, 9–18.
Résumé: Isomerization, ionization and fragmentation of molecular compounds in the interstellar medium can be triggered by stellar radiation and cosmic rays. In the present contribution, we examine the propensity for isomerization and the relative stability of aromatic rings in the pyrene and coronene molecules at various degrees of dehydrogenation by means of molecular modeling. Using the AIREBO reactive force field and advanced Monte Carlo techniques such as the Wang–Landau method based on suitable order parameters, entire free-energy profiles describing the isomerization pathways and equilibrium properties were calculated as a function of temperature or total energy. We generally find that hydrogenation significantly stabilizes the fully polycyclic aromatic hydrocarbon (PAH) structure, even though local dehydrogenation next to an aromatic ring favors ring opening. The formation of pentagonal rings, a typical defect motif in the polycyclic carbon skeleton, is predicted to be actually competitive with the loss of a hydrogen atom. Our investigation emphasizes the likely presence of defects in astrophysical PAHs, whose spectral features remain to be better characterized and understood.
|
|
|
Pirali, O., Goubet, M., Boudon, V., D’Accolti, L., Fusco, C., & Annese, C. (2017). Characterization of isolated 1-aza-adamantan-4-one (C9H13NO) from microwave, millimeter-wave and infrared spectroscopy supported by electronic structure calculations. Journal of Molecular Spectroscopy, 338(Supplement C), 6–14.
|
|
|
Roucou, A., Dhont, G., Cuisset, A., Martin-Drumel, M. - A., Thorwirth, S., Fontanari, D., & Meerts, W. L. (2017). High resolution study of the ν2 and ν5 rovibrational fundamental bands of thionyl chloride: Interplay of an evolutionary algorithm and a line-by-line analysis. The Journal of Chemical Physics, 147(5), 054303.
|
|
Vanfleteren, T., Földes, T., Herman, M., Liévin, J., Loreau, J., & Coudert, L. H. (2017). Experimental and theoretical investigations of H2O–Ar. The Journal of Chemical Physics, 147(1), 014302.
Résumé: We have used continuous-wave cavity ring-down spectroscopy to record the spectrum of H2O–Ar
H2O–Ar in the 2OH excitation range of H2O. 24 sub-bands have been observed. Their rotational structure (Trot = 12 K) is analyzed and the lines are fitted separately for ortho and para species together with microwave and far infrared data from the literature, with a unitless standard deviation σ=0.98 and 1.31, respectively. Their vibrational analysis is supported by a theoretical input based on an intramolecular potential energy surface obtained through ab initio calculations and computation of the rotational energy of sub-states of the complex with the water monomer in excited vibrational states up to the first hexad. For the ground and (010) vibrational states, the theoretical results agree well with experimental energies and rotational constants in the literature. For the excited vibrational states of the first hexad, they guided the assignment of the observed sub-bands. The upper state vibrational predissociation lifetime is estimated to be 3 ns from observed spectral linewidths.
|
|
Yalouz, S., Falvo, C., & Pouthier, V. (2017). The excitonic qubit coupled with a phonon bath on a star graph: anomalous decoherence and coherence revivals. Quantum Information Processing, 16(6), 143.
Résumé: Based on the operatorial formulation of perturbation theory, the dynamical properties of a Frenkel exciton coupled with a thermal phonon bath on a star graph are studied. Within this method, the dynamics is governed by an effective Hamiltonian which accounts for exciton–phonon entanglement. The exciton is dressed by a virtual phonon cloud, whereas the phonons are dressed by virtual excitonic transitions. Special attention is paid to the description of the coherence of a qubit state initially located on the central node of the graph. Within the nonadiabatic weak coupling limit, it is shown that several timescales govern the coherence dynamics. In the short time limit, the coherence behaves as if the exciton was insensitive to the phonon bath. Then, quantum decoherence takes place, this decoherence being enhanced by the size of the graph and by temperature. However, the coherence does not vanish in the long time limit. Instead, it exhibits incomplete revivals that occur periodically at specific revival times and it shows almost exact recurrences that take place at particular super-revival times, a singular behavior that has been corroborated by performing exact quantum calculations.
|
|
Yalouz, S., Pouthier, V., & Falvo, C. (2017). Exciton-phonon dynamics on complex networks: Comparison between a perturbative approach and exact calculations. Pre, 96(2), 022304.
Résumé: A method combining perturbation theory with a simplifying ansatz is used to describe the exciton-phonon dynamics in complex networks. This method, called PT, is compared to exact calculations based on the numerical diagonalization of the exciton-phonon Hamiltonian for eight small-sized networks. It is shown that the accuracy of
PT depends on the nature of the network, and three different situations were identified. For most graphs,
PT yields a very accurate description of the dynamics. By contrast, for the Wheel graph and the Apollonian network, PT reproduces the dynamics only when the exciton occupies a specific initial state. Finally, for the complete graph, PT breaks down. These different behaviors originate in the interplay between the degenerate nature of the excitonic energy spectrum and the strength of the exciton-phonon interaction so that a criterion is established to determine whether or not PT is relevant. When it succeeds, our study shows the undeniable advantage of PT in that it allows us to perform very fast simulations when compared to exact calculations that are restricted to small-sized networks.
|
|
