Peer-reviewed Publications |
Aguillon, F., Marinica, D. C., & Borisov, A. G. (2022). Atomic-scale control of plasmon modes in graphene nanoribbons. Phys. Rev. B, 105, L081401.
Résumé: We address the possibility of atomic-scale control of the plasmon modes of graphene nanostructures. Using the time-dependent many-body approach we show that for the zigzag and armchair nanoribbons, the single carbon atom vacancy results in “on” and “off” switching of the longitudinal plasmon modes or in a change of their frequency. The effect stems from the robust underlying physical mechanism based on the strong scattering of the two-dimensional (2D) electrons on the vacancy defects in graphene lattice. Thus our findings establish a platform for optical response engineering or sensing in 2D materials.
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Autuori A, Platzer D, Lejman M, Gallician G, Maeder L, Covolo A, Bosse L, Dalui M, Bresteau D, Hergott JF, Tcherbakoff O, Marroux HJB, Loriot V, Lepine F, Poisson L, Taieb R, Caillat J, & Salieres P. (2022). Anisotropic dynamics of two-photon ionization: An attosecond movie of photoemission. Sci Adv, 8(12), eabl7594.
Résumé: Imaging in real time the complete dynamics of a process as fundamental as photoemission has long been out of reach because of the difficulty of combining attosecond temporal resolution with fine spectral and angular resolutions. Here, we achieve full decoding of the intricate angle-dependent dynamics of a photoemission process in helium, spectrally and anisotropically structured by two-photon transitions through intermediate bound states. Using spectrally and angularly resolved attosecond electron interferometry, we characterize the complex-valued transition probability amplitude toward the photoelectron quantum state. This allows reconstructing in space, time, and energy the complete formation of the photoionized wave packet.
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Babaze, A., Ogando, E., Stamatopoulou, P. E., Tserkezis, C., Mortensen, N. A., Aizpurua, J., Borisov, A. G., & Esteban, R. (2022). Quantum surface effects in the electromagnetic coupling between a quantum emitter and a plasmonic nanoantenna: time-dependent density functional theory vs. semiclassical Feibelman approach. Opt. Express, 30(12), 21159–21183.
Résumé: We use time-dependent density functional theory (TDDFT) within the jellium model to study the impact of quantum-mechanical effects on the self-interaction Green’s function that governs the electromagnetic interaction between quantum emitters and plasmonic metallic nanoantennas. A semiclassical model based on the Feibelman parameters, which incorporates quantum surface-response corrections into an otherwise classical description, confirms surface-enabled Landau damping and the spill out of the induced charges as the dominant quantum mechanisms strongly affecting the nanoantenna–emitter interaction. These quantum effects produce a redshift and broadening of plasmonic resonances not present in classical theories that consider a local dielectric response of the metals. We show that the Feibelman approach correctly reproduces the nonlocal surface response obtained by full quantum TDDFT calculations for most nanoantenna–emitter configurations. However, when the emitter is located in very close proximity to the nanoantenna surface, we show that the standard Feibelman approach fails, requiring an implementation that explicitly accounts for the nonlocality of the surface response in the direction parallel to the surface. Our study thus provides a fundamental description of the electromagnetic coupling between plasmonic nanoantennas and quantum emitters at the nanoscale.
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Boulet, C., & Ma, Q. (2022). Line coupling and line mixing effects on calculated widths of symmetric-top molecules with the k-degeneracy: A theoretical study of N2-, O2-, and air-broadened lines of CH3I. Journal of Quantitative Spectroscopy and Radiative Transfer, 288, 108273.
Résumé: Calculations of the N2-, O2-, and air-broadened widths, together with their temperature dependence exponents have been made for transitions of CH3I in the ν5 and ν6 bands. The calculations are based on a semi-classical line shape formalism developed by the current authors through modifying and refining the Robert-Bonamy formalism. In recent years, we have applied this formalism for linear molecules, symmetric-top molecules with inversion symmetry, and asymmetric-top molecules. For symmetric-top molecules with the k degeneracy such as CH3I, the formalism has a new feature. In this case, one should consider each of the CH3I transitions labeled by ki or f ≠ 0 as a doublet. Then, one needs to consider the effects of the line mixing process between these two components. Comparisons of our theoretical predictions with some data available demonstrate a very reasonable agreement. Finally we propose new experiments at higher perturber pressures that would enable one to check the theoretically calculated relaxation matrices and to extend the analysis to the inter-doublet mixing effects.
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Briant M, Mestdagh JM, Gaveau MA, & Poisson L. (2022). Reaction dynamics within a cluster environment. Phys Chem Chem Phys, 24, 9807–9835.
Résumé: This perspective article reviews experimental and theoretical works where rare gas clusters and helium nanodroplets are used as a nanoreactor to investigate chemical dynamics in a solvent environment. A historical perspective is presented first followed by specific considerations on the mobility of reactants within these reaction media. The dynamical response of pure clusters and nanodroplets to photoexcitation is shortly reviewed before examining the role of the cluster (or nanodroplet) degrees of freedom in the photodynamics of the guest atoms and molecules.
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Buntine, J. T., Carrascosa, E., Bull, J. N., Jacovella, U., Cotter, M. I., Watkins, P., Liu, C., Scholz, M. S., Adamson, B. D., Marlton, S. J. P., & Bieske, E. J. (2022). An ion mobility mass spectrometer coupled with a cryogenic ion trap for recording electronic spectra of charged, isomer-selected clusters. Review of Scientific Instruments, 93, 043201.
Résumé: Infrared and electronic spectra are indispensable for understanding the structural and energetic properties of charged molecules and clusters in the gas phase. However, the presence of isomers can potentially complicate the interpretation of spectra, even if the target molecules or clusters are mass-selected beforehand. Here, we describe an instrument for spectroscopically characterizing charged molecular clusters that have been selected according to both their isomeric form and their mass-to-charge ratio. Cluster ions generated by laser ablation of a solid sample are selected according to their collision cross sections with helium buffer gas using a drift tube ion mobility spectrometer and their mass-to-charge ratio using a quadrupole mass filter. The mobility- and mass-selected target ions are introduced into a cryogenically cooled, three-dimensional quadrupole ion trap where they are thermalized through inelastic collisions with an inert buffer gas (He or He/N2 mixture). Spectra of the molecular ions are obtained by tagging them with inert atoms or molecules (Ne and N2), which are dislodged following resonant excitation of an electronic transition, or by photodissociating the cluster itself following absorption of one or more photons. An electronic spectrum is generated by monitoring the charged photofragment yield as a function of wavelength. The capacity of the instrument is illustrated with the resonance-enhanced photodissociation action spectra of carbon clusters (Cn+) and polyacetylene cations (HC2nH+) that have been selected according to the mass-to-charge ratio and collision cross section with He buffer gas and of mass-selected Au+2 and Au2Ag+ clusters.
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Buntine, J. T., Carrascosa, E., Bull, J. N., Muller, G., Jacovella, U., Glasson, C. R., Vamvounis, G., & Bieske, E. J. (2022). Photo-induced 6π-electrocyclisation and cycloreversion of isolated dithienylethene anions. Phys. Chem. Chem. Phys., in press.
Résumé: The diarylethene chromophore is commonly used in light-triggered molecular switches. The chromophore undergoes reversible 6π-electrocyclisation (ring closing) and cycloreversion (ring opening) reactions upon exposure to UV and visible light, respectively, providing bidirectional photoswitching. Here, we investigate the gas-phase photoisomerisation of meta- (m) and para- (p) substituted dithienylethene carboxylate anions (DTE−) using tandem ion mobility mass spectrometry coupled with laser excitation. The ring-closed forms of p-DTE− and m-DTE− are found to undergo cycloreversion in the gas phase with maximum responses associated with bands in the visible (λmax ≈ 600 nm) and the ultraviolet (λmax ≈ 360 nm). The ring-open p-DTE− isomer undergoes 6π-electrocyclisation in the ultraviolet region at wavelengths shorter than 350 nm, whereas no evidence is found for the corresponding electrocyclisation of ring-open m-DTE−, a situation attributed to the fact that the antiparallel geometry required for electrocyclisation of m-DTE− is energetically disfavoured. This highlights the influence of the carboxylate substitution position on the photochemical properties of DTE molecules. We find no evidence for the formation in the gas phase of the undesirable cyclic byproduct, which causes fatigue of DTE photoswitches in solution.
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Chen, N. L., Gans, B., Hartweg, S., Garcia, G. A., Boyé-Péronne, S., & Loison, J. - C. (2022). Photoionization spectroscopy of the SiH free radical in the vacuum-ultraviolet range. The Journal of Chemical Physics, 157(1), 014303.
Résumé: The first measurement of the photoelectron spectrum of the silylidyne free radical, SiH, is reported between 7 and 10.5 eV. Two main photoionizing transitions involving the neutral ground state, X+ 1Σ+ ← X 2 Π and a+ 3Π ← X 2 Π, are assigned by using ab initio calculations. The corresponding adiabatic ionization energies are derived, IEad (X+ 1Σ+ ) = 7.934(5) eV and IEad (a+ 3Π) = 10.205(5) eV, in good agreement with our calculated values and the previous determination by Berkowitz et al. [J. Chem. Phys. 86, 1235 (1987)] from a photoionization mass spectrometric study. The photoion yield of SiH recorded in this work exhibits a dense autoionization landscape similar to that observed in the case of the CH free radical [Gans et al., J. Chem. Phys. 144, 204307 (2016)].
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Drozdovskaya, M. N., Coudert, L. H., Margulès, L., Coutens, A., Jørgensen, J. K., & Manigand, S. (2022). Successive deuteration in low-mass star-forming regions: The case of D2-methanol (CHD2OH) in IRAS 16293-2422. A&A, 659, A69.
Résumé: Context. Di-deuterated molecules are observed in the earliest stages of star formation at abundances of a few percent relative to their nondeuterated isotopologs, which is unexpected considering the scarcity of deuterium in the interstellar medium. With sensitive observations leading to the detection of a steadily increasing number of di-deuterated species, it is becoming possible to explore successive deuteration chains.
Aims. The accurate quantification of the column density of di-deuterated methanol is a key piece of the puzzle that is missing in the otherwise thoroughly constrained family of D-bearing methanol in the deeply embedded low-mass protostellar system and astrochemical template source IRAS 16293-2422. A spectroscopic dataset for astrophysical purposes was built for CHD2OH and made publicly available to facilitate the accurate characterization of this species in astrochemical surveys.
Methods. The newly computed line list and partition function were used to search for CHD2OH toward IRAS 16293-2422 A and B in data from the Atacama Large Millimeter/submillimeter Array (ALMA) Protostellar Interferometric Line Survey (PILS). Only nonblended, optically thin lines of CHD2OH were used for the synthetic spectral fitting.
Results. The constructed spectroscopic database contains line frequencies and strengths for 7417 transitions in the 0–500 GHz frequency range. ALMA-PILS observations in the 329–363 GHz range were used to identify 105 unique, nonblended, optically thin line frequencies of CHD2OH for synthetic spectral fitting. The derived excitation temperatures and column densities yield high D/H ratios of CHD2OH in IRAS 16293-2422 A and B of 7.5 ± 1.1% and 7.7 ± 1.2%, respectively.
Conclusions. Deuteration in IRAS 16293-2422 is not higher than in other low-mass star-forming regions (L483, SVS13-A, NGC 1333-IRAS2A, -IRAS4A, and -IRAS4B). Di-deuterated molecules consistently have higher D/H ratios than their mono-deuterated counterparts in all low-mass protostars, which may be a natural consequence of H–D substitution reactions as seen in laboratory experiments. The Solar System’s natal cloud, as traced by comet 67P/Churyumov–Gerasimenko, may have had a lower initial abundance of D, been warmer than the cloud of IRAS 16293-2422, or been partially reprocessed. In combination with accurate spectroscopy, a careful spectral analysis, and the consideration of the underlying assumptions, successive deuteration is a robust window on the physicochemical provenance of star-forming systems.
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Fakhardji, W., Boulet, C., Tran, H., & Hartmann, J. - M. (2022). Direct calculations of the CH4+CO2 far infrared collision-induced absorption. Journal of Quantitative Spectroscopy and Radiative Transfer, 283, 108148.
Résumé: We present computations, solely using input data from the literature and thus free of any adjusted parameter, of the far infrared collision-induced absorption (CIA) by interacting CH4 and CO2 molecules. They are based on classical molecular dynamics simulations (CMDS) of the rotational and translational motions of the molecules made using an accurate ab initio CH4-CO2 anisotropic intermolecular potential, and on a long-range expansion of the interaction-induced dipole. Various desymmetrization procedures, which all ensure detailed balance of the spectral density function are a posteriori applied to the CMDS results. The comparison with the available measurements, which have been collected at room temperature, show that a good agreement can be obtained without introducing any ad hoc short-range dipole components, and it enables to point out the limits of some of the desymmetrization procedures. Tests are also made of the so-called "isotropic approximation", which point out its strong limits, since it leads to large underestimations of the CIA, and question previous computations made using an isotropic potential and long-range expansion of the induced dipole complemented by ad hoc contributions at short distances. Finally, the temperature dependence of the CIA is predicted for applications to planetary atmospheres.
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Harper, O. J., Chen, N. L., Boyé-Péronne, S., & Gans, B. (2022). Pulsed-Ramped-Field-Ionization ZEro-Kinetic-Energy PhotoElectron Spectroscopy: a methodological advance. Phys. Chem. Chem. Phys., 24, 2777.
Résumé: A new experimental method has been developed to record photoelectron spectra based on the well-established pulsed-field-ionization zero-kinetic-energy photoelectron spectroscopy technique and inspired by the data treatment employed in slow photoelectron spectroscopy. This method has been successfully applied to two well-known systems: the X+2Πg, 1/2 (v+=0) ← X 1Σ+g (v=0) and the X+1Σ+ (v+=2) ← X 2Π1/2 (v=0) ionizing transitions of CO2 and NO, respectively. The first results highlight several advantages of our technique such as an improved signal-to-noise ratio without degrading the spectral resolution and a direct field-free energy determination. The data obtained for NO indicate that this method might be useful for studying field-induced autoionization processes.
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Hearne, T. S., Mammez, M. - H., Mammez, D., Martin-Drumel, M. - A., Roy, P., Pirali, O., Eliet, S., Barbieri, S., Hindle, F., Mouret, G., & Lampin, J. - F. (2022). Unlocking synchrotron sources for THz spectroscopy at sub-MHz resolution. Opt. Express, 30(5), 7372–7382.
Résumé: Synchrotron radiation (SR) has proven to be an invaluable contributor to the field of molecular spectroscopy, particularly in the terahertz region (1-10 THz) where its bright and broadband properties are currently unmatched by laboratory sources. However, measurements using SR are currently limited to a resolution of around 30 MHz, due to the limits of Fourier-transform infrared spectroscopy. To push the resolution limit further, we have developed a spectrometer based on heterodyne mixing of SR with a newly available THz molecular laser, which can operate at frequencies ranging from 1 to 5.5 THz. This spectrometer can record at a resolution of 80 kHz, with 5 GHz of bandwidth around each molecular laser frequency, making it the first SR-based instrument capable of sub-MHz, Doppler-limited spectroscopy across this wide range. This allows closely spaced spectral features, such as the effects of internal dynamics and fine angular momentum couplings, to be observed. Furthermore, mixing of the molecular laser with a THz comb is demonstrated, which will enable extremely precise determinations of molecular transition frequencies.
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Jacovella, U., Buntine, J. T., Cotter, M., Muller, G., Scholz, M. S., & Dartois, E. (2022). On the possible contribution of cationic oxygenated carbon chains CnO+, HCnO+, and OCnO+ (n = 4 − 9) to the diffuse interstellar bands. Mon Not R Astron Soc, 511(4), 5171–5179.
Résumé: Only 4 of the diffuse interstellar bands (DIBs) are currently accounted for, ascribed to electronic transitions of C_{60}^+. Investigations into carriers of other DIBs historically focus on charged and neutral hydrocarbons, and little information is available regarding oxygenated carbon and hydrocarbon species that result from the two most abundant heavy elements in the interstellar medium, C and O. In this study, we assess whether CnO+, HCnO+, and OCnO+ (n = 4 − 9) cations are viable candidates to account for DIBs using both density-functional theory (DFT) and coupled cluster single-double and perturbative triple theory, CCSD(T). For these species, the linear structures are the most stable isomers with the lowest dissociation threshold corresponding to CO loss. Optical absorptions of the oxygenated carbon chain cations are characterized by calculated vertical excitation wavelengths and their corresponding oscillator strengths using the equation-of-motion CCSD (EOM-CCSD) method. Aside from HC4O+ and HC2n + 1O+, all of the species considered in this study have calculated electronic transitions that lie in the visible or near-infrared spectral regions. Minimal column densities necessary for these cations to account for DIBs have been estimated. Based on present results and the known column densities for neutral oxygenated carbon chains in TMC-1, the growth rate of charged O-bearing carbon chains via ion-neutral reaction mechanisms is judged to be too low to form a sufficient population to give rise to DIBs.
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Jacovella, U., Hansen, C. S., Giuliani, A., Trevitt, A. J., & Nahon, L. (2022). UV/VUV photo-processing of protonated N-hetero(poly)acenes. Mon Not R Astron Soc, 511(4), 5656–5660.
Résumé: N-heterocycles are suspected to play an important role in the chemical origin of life. Despite their detection in meteorites and in Titan’s atmosphere, their extra-terrestrial chemical formation networks remain elusive. Furthermore N-heterocyclics are undetected in the interstellar medium. This paper assesses the photostability of protonated N-hetero(poly)acenes after UV and VUV excitation. It provides information on their ability to retain the N atom into the cycle to generate larger N-containing species or functionalized N-heterocyles. Protonated N-hetero(poly)acenes were generated using electrospray ionization and injected into a linear ion trap where they were irradiated by radiation of 4.5 to 10 eV using the DESIRS beamline at the synchrotron SOLEIL. The photodissociation action spectra of protonated pyridine, quinoline, isoquinoline, and acridine were measured by recording the photofragment yields as a function of photon energy. The four systems exhibit dissociation channels associated with H2 and HCN/HNC loss but with different branching ratios. The results indicate that increasing the size of the N-hetero(poly)acenes increases the chance of retaining the N atom in the larger fragment ion after photodissociation but it remains that all the protonated N-hetero(poly)acenes studied lose their N atom at part of a small neutral photofragment, with high propensity. Therefore, protonated N-hetero(poly)acenes in interstellar space are unlikely precursors to form larger N-containing species. However, protonated pyridine, quinoline, isoquinoline, and acridine are most likely to retain their N atoms in planetary atmospheres where UV radiation at the planet’s surface is typically restricted to wavelengths greater than 200 nm – suggesting such environments are possible substrates for prebiotic chemistry.
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Jacovella, U., Noble, J. A., Guliani, A., Hansen, C. S., Trevitt, A. J., Mouzay, J., Couturier-Tamburelli, I., Pietri, N., & Nahon, L. (2022). Ultraviolet and vacuum ultraviolet photo-processing of protonated benzonitrile (C6H5CNH+). A&A, 657, A85.
Résumé: Context. The recent detection in pre-stellar sources of cyano-substituted and pure hydrocarbon cycles has emphasized the importance of aromatic chemistry in the earliest stages of star formation. Ultraviolet (UV) and vacuum-UV (VUV) radiation is ubiquitous in space and thus the photo-processing of small cyclic ions may open a window onto rich chemical networks and lead to the formation of larger aromatics in space.
Aims. The aim is to investigate the fate of protonated benzonitrile species after UV and VUV photoexcitation and the subsequent potential impact on stellar and interstellar chemistry.
Methods. Protonated benzonitrile was isolated in a linear ion trap prior to irradiation with UV and VUV radiation (4.5–13.6 eV) from the DESIRS beamline at synchrotron SOLEIL. The study was extended down to 3.5 eV using a cryogenic Paul ion trap coupled to an OPO laser at the PIIM laboratory. Photodissociation action spectra were obtained by monitoring the photofragment yields as a function of photon energy.
Results. The UV/VUV photodissociation action spectra of protonated benzonitrile show structured bands from 3.8 to 9 eV. The primary dissociation channel of protonated benzonitrile corresponds to HCN/HNC loss and formation of the phenylium cation (C6H5+); whereas at high energies, a minor channel is observed that correlates with HC3N loss and formation of C4H5+.
Conclusions. The UV and VUV photodestruction of protonated benzonitrile leads to the formation of a highly reactive cationic species, C6H5+, predicted to be an important precursor of larger aromatic molecules in space, such as polycyclic aromatic hydrocarbons. The inclusion of C6H5+ – a precursor of benzene and, by extension, of benzonitrile – as the result of formation via the photodissociation of protonated benzonitrile in current astrochemical models could improve the predicted abundance of benzonitrile, which is currently underestimated.
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Le Sech, C. (2022). Changes induced in a covalent bond confined in a structured cavity. Chemical Physics Letters, 791, 139396.
Résumé: A simple correlated wave function is proposed to study the confined hydrogen molecule. Three confinement structural forms are considered: a hard sphere, a cone, and a composite sphere-cone to simulate the effects of a structured cavity. The changes in the molecular energy, in particular the vibration, are calculated through a variational non Born-Oppenheimer approach.
In all three cases, a steep rise in the molecule energy is observed. The composite sphere-cone structure is the most efficient. A compression/relaxation cycle in such a cavity, produced by the conformational molecular dynamics, augments the energy. This finding could be of interest in chemical catalysis in supramolecular cavities.
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Lietard A, Piani G, Pollet R, Soep B, Mestdagh JM, & Poisson L. (2022). Excited state dynamics of normal dithienylethene molecules either isolated or deposited on an argon cluster. Phys Chem Chem Phys, 24, 10588–10598.
Résumé: Real-time dynamics of the electronically excited open-ring isomer of 1,2-bis(2-methylbenzo[b]thiophen-3-yl)perfluorocyclopentene (BTF6) and 1,2-bis(2,4-dimethyl-5-phenyl-3-thienyl)perfluorocyclopentene (PTF6) molecules was investigated using a set-up that associates a molecular beam, femtosecond lasers and velocity map imaging. The molecules were either free in the gas phase or bound to an argon cluster. DFT and TDDFT calculations were performed on BTF6. The calculated vertical excitation energies indicate an excitation by the pump laser towards a superposition of S5 and S6 states. The free molecule dynamics was found to follow a three wavepacket model. One describes the parallel conformer (P) of these molecules. It is unreactive with respect to the ring closure reaction which is responsible for the photochromic property of these molecules. It has no observable decay at the experiment time scale (up to 350 ps). The other two wavepackets describe the reactive antiparallel conformer (AP). They are formed by an early splitting of the wavepacket that was launched initially by the pump laser. They can be considered as generated by excitation of different, essentially uncoupled, deformation modes. They subsequently evolve along independent pathways. One is directed ballistically towards a conical intersection (CI) and decays through the CI to a potential energy surface where it can no longer be detected. The other fraction of the wavepacket decays also towards undetected states but in this case the driving mechanism is a non-adiabatic electronic relaxation within a potential well of the energy surfaces where it was launched. When BTF6 and PTF6 molecules are bound to an argon cluster, the same three wavepacket model applies. The vibronic relaxation timespan is enhanced by a factor 5 and a larger fraction of AP conformers follows this pathway. In contrast, the time constant associated with the ballistic movement is enhanced by only a factor of 2.
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Mammez, M. - H., Buchanan, Z., Pirali, O., Martin-Drumel, M. - A., Turut, J., Ducournau, G., Eliet, S., Hindle, F., Barbieri, S., Roy, P., Mouret, G., & Lampin, J. - F. (2022). Optically Pumped Terahertz Molecular Laser: Gain Factor and Validation up to 5.5 THz. Adv. Photonics Res., , 2100263.
Résumé: Quantum cascade laser-pumped terahertz (THz) gas lasers are at the edge of revolutionizing THz science where powerful yet tunable sources have long been lacking. Maybe one of the last remaining drawbacks to a wider use of these instruments lies in the lack of available databases of potentially lasing transitions for users. A new figure of merit, the molecular gain?factor is proposed, that allows to discriminate transitions by their lasing potential. Using this factor, catalogs of THz laser lines of ammonia, both 14NH3 and 15NH3, up to 10?THz are reported. Demonstration of the use of these two catalogs, and of the pertinence of the molecular gain?factor, is made by experimentally observing 32 laser lines of 14NH3 and 5 lines of 15NH3 up to 5.5?THz. Prospects to generalize the use of this molecular gain?factor to a wide range of molecules are discussed.
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Mandal S, Gatti F, Bindech O, Marquardt R, & Tremblay JC. (2022). Multidimensional stochastic dissipative quantum dynamics using a Lindblad operator. J Chem Phys, 156, 094109.
Résumé: In this paper, multidimensional dissipative quantum dynamics is studied within a system-bath approach in the Markovian regime using a model Lindblad operator. We report on the implementation of a Monte Carlo wave packet algorithm in the Heidelberg version of the Multi-Configuration Time-Dependent Hartree (MCTDH) program package, which is henceforth extended to treat stochastic dissipative dynamics. The Lindblad operator is represented as a sum of products of one-dimensional operators. The new form of the operator is not restricted to the MCTDH formalism and could be used with other multidimensional quantum dynamical methods. As a benchmark system, a two-dimensional coupled oscillators model representing the internal stretch and the surface-molecule distance in the O2/Pt(111) system coupled to a Markovian bath of electron-hole-pairs is used. The simulations reveal the interplay between coherent intramolecular coupling due to anharmonic terms in the potential and incoherent relaxation due to coupling to an environment. It is found that thermalization of the system can be approximately achieved when the intramolecular coupling is weak.
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Matthaei CT, Mukhopadhyay DP, Roder A, Poisson L, & Fischer I. (2022). Photodissociation of the trichloromethyl radical: photofragment imaging and femtosecond photoelectron spectroscopy. Phys Chem Chem Phys, 2(24), 928–940.
Résumé: Halogen-containing radicals play a key role in catalytic reactions leading to stratospheric ozone destruction, thus their photochemistry is of considerable interest. Here we investigate the photodissociation dynamics of the trichloromethyl radical, CCl3 after excitation in the ultraviolet. While the primary processes directly after light absorption are followed by femtosecond-time resolved photoionisation and photoelectron spectroscopy, the reaction products are monitored by photofragment imaging using nanosecond-lasers. The dominant reaction is loss of a Cl atom, associated with a CCl2 fragment. However, the detection of Cl atoms is of limited value, because in the pyrolysis CCl2 is formed as a side product, which in turn dissociates to CCl + Cl. We therefore additionally monitored the molecular fragments CCl2 and CCl by photoionisation at 118.2 nm and disentangled the contributions from various processes. A comparison of the CCl images with control experiments on CCl2 suggest that the dissociation to CCl + Cl2 contributes to the photochemistry of CCl3.
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Raphaël Thon, Wutharath Chin, Didier Chamma, Mindaugas Jonusas, Jean-Pierre Galaup, & Claudine Crépin. (2022). Vibrational dynamics of iron pentacarbonyl in cryogenic matrices. J Chem Phys, 156(2), 024301-12.
Résumé: Iron pentacarbonyl is a textbook example of fluxionality. We trap the molecule in cryogenic matrices to study the vibrational dynamics of
CO stretching modes involved in the fluxional rearrangement. The infrared spectrum in Ar and N2 is composed of about ten narrow bands
in the spectral range of interest, indicating the population of various lattice sites and a lowering of the molecular symmetry in the trapping
sites. The vibrational dynamics is explored by means of infrared stimulated photon echoes at the femtosecond scale. Vibrational dephasing
and population relaxation times are obtained. The non-linear signals exhibit strong oscillations useful to disentangle the site composition
of the absorption spectrum. The population relaxation involves at least two characteristic times. An evolution of the photon echo signals
with the waiting time is observed. The behavior of all the signals can be reproduced within a simple model that describes the population
relaxation occurring in two steps: relaxation of v = 1 (population time T1 < 100 ps) and return to v = 0 (recovery time > 1 ns). These two steps
explain the evolution of the oscillations with the waiting time in the photon echo signals. These results discard fluxional rearrangement on
the time scale of hundreds of ps in our samples. Dephasing times are of the same order of magnitude as T1: dephasing processes due to the
matrix environment are rather inefficient. The photon echo experiments also reveal that intermolecular resonant vibrational energy transfers
between guest molecules occur at the hundreds of ps time scale in concentrated samples (guest/host > 104).
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Rosławska, A., Neuman, T., Doppagne, B., Borisov, A. G., Romeo, M., Scheurer, F., Aizpurua, J., & Schull, G. (2022). Mapping Lamb, Stark, and Purcell Effects at a Chromophore-Picocavity Junction with Hyper-Resolved Fluorescence Microscopy. Phys. Rev. X, 12, 011012.
Résumé: The interactions of the excited states of a single chromophore with static and dynamic electric fields spatially varying at the atomic scale are investigated in a joint experimental and theoretical effort. In this configuration, the spatial extension of the fields confined at the apex of a scanning tunneling microscope tip is smaller than that of the molecular exciton, a property used to generate fluorescence maps of the chromophore with intramolecular resolution. Theoretical simulations of the electrostatic and electrodynamic interactions occurring at the picocavity junction formed by the chromophore, the tip, and the substrate reveal the key role played by subtle variations of Purcell, Lamb, and Stark effects. They also demonstrate that hyper-resolved fluorescence maps of the line shift and linewidth of the excitonic emission can be understood as images of the static charge redistribution upon electronic excitation of the molecule and as the distribution of the dynamical charge oscillation associated with the molecular exciton, respectively.
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Sathanikan, A., Ceccone, G., Bañuls-Ciscar, J., Pan, M., Kamal, F., Bsaibess, T., Gaucher, A., Prim, D., Méallet-Renault, R., Colpo, P., Amigoni, S., Guittard, F., & Darmanin, T. (2022). A bioinspired approach to fabricate fluorescent nanotubes with strong water adhesion by soft template electropolymerization and post-grafting. Journal of Colloid and Interface Science, 606(1), 236–247.
Résumé: Hypothesis
In this original work, we aim to control both the surface wetting and fluorescence properties of extremely ordered and porous conducting polymer nanotubes prepared by soft template electropolymerization and post-grafting. For reaching this aim, various substituents of different hydrophobicity and fluorescence were post-grafted and the post-grafting yields were evaluated by surface analyses. We show that the used polymer is already fluorescent before post-grafting while the post-grafting yield and as a consequence the surface hydrophobicity highly depend on the substituent.
Experiments
Here, we have chosen to chemically grafting various fluorinated and aromatic substituents using a post-grafting in order to keep the same surface topography. Flat conducting polymer surfaces with similar properties have been also prepared for determining the surface energy with the Owens-Wendt equation and estimating the post-grafting yield by X-ray Photoemission Spectroscopy (XPS) and Time of Flight Secondary Emission Spectrometry (ToF-SIMS). For example, using fluorinated chains of various length (C4F9, C6F13 and C8F17), it is demonstrated that the surface hydrophobicity and oleophobicity do not increase with the fluorinated chain length due to the different post-grafting yields and because of the presence of nanoroughness after post-grafting.
Findings
These surfaces have high apparent water contact angle up to 130.5° but also strong water adhesion, comparable to rose petal effect even if there are no nanotubes on petal surface. XPS and ToF-SIMS analyses provided a detailed characterisation of the surface chemistry with a qualitative classification of the grafted surfaces (F6 > F4 > F8). SEM analysis shows that grafting does not alter the surface morphology. Finally, fluorescence analyses show that the polymer surfaces before post-treatment are already nicely fluorescent. Although the main goal of this paper was and is to understand the role of surface chemistry in tailoring the wetting properties of these surfaces rather than provide specific application examples, we believe that the obtained results can help the development of specific nanostructured materials for potential applications in liquid transport, or in stimuli responsive antimicrobial surfaces.
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Si, Y., Grazon, C., Clavier, G., Audibert, J. - F., Sclavi, B., & Méallet-Renault, R. (2022). FRET-mediated quenching of BODIPY fluorescent nanoparticles by methylene blue and its application to bacterial imaging. Photochemical & Photobiological Sciences, in press.
Résumé: High resolution and a good signal to noise ratio are a requirement in cell imaging. However, after labelling with fluorescent entities, and after several washing steps, there is often an unwanted fluorescent background that reduces the images resolution. For this purpose, we developed an approach to remove the signal from extra-cellular fluorescent nanoparticles (FNPs) during bacteria imaging, without the need for any washing steps. Our idea is to use methylene blue to quench > 90% of the emission of BODIPY-based fluorescent polymer nanoparticle by a FRET process. This “Hide-and-Seek Game” approach offers a novel strategy to apply fluorescence quenching in bioimaging to improve image accuracy.
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Szczepaniak, U., Kolos, R., Guillemin, J. - C., & Crépin, C. (2022). Phosphorescence of C5N– in rare gas solids. Photochem, 2, 263–271.
Résumé: Phosphorescence of C5N– was discovered following the ArF-laser (193 nm) photolysis of cy-anodiacetylene (HC5N) isolated in cryogenic argon, krypton and xenon matrices. This visible emission, with the origin around 460 nm, is vibrationally resolved, permitting the measurement of frequencies for eight ground-state fundamental vibrational modes, including the three known from previous IR absorption studies. Phosphorescence lifetime amounts to tens or even hun-dreds of ms depending on the matrix host; it is 5 times longer than in the case of HC5N.
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Tamassia, F., Bizzocchi, L., Melosso, M., Martin-Drumel, M. - A., Pirali, O., Pietropolli Charmet, A., Canè, E., Dore, L., Gordon, I. E., Guillemin, J. - C., Giuliano, B. M., Caselli, P., Alessandrini, S., Barone, V., & Puzzarini, C. (2022). Synchrotron-based far-infrared spectroscopy of HC3N: Extended ro-vibrational analysis and new line list up to 3360 cm−1. Journal of Quantitative Spectroscopy and Radiative Transfer, 279, 108044.
Résumé: The far-infrared spectrum of HC3N has been recorded at high resolution between 70 and 500 cm−1using synchrotron radiation. Four prominent features, i.e., ν7, ν6−ν7, ν4−ν6, and 2ν7 have been identified in the spectrum together with many associated hot bands. In addition, rotational transitions for the interacting v4=v7=1, (v6=2,v7=1), (v5=1,v7=2), and v7=5 vibrationally excited states have been recorded in the millimeter/submillimeter region. The newly assigned transitions, together with those reported previously, form a comprehensive data set including about 17 000 transitions, which involves almost all the vibrational states of HC3N lying below 1300 cm−1 plus some excited states with energies between 2075 and 3550 cm−1. These data have been fitted to an effective Hamiltonian which takes into account rotational and vibrational l-type resonance effects, together with a number of anharmonic interaction terms. On average, all the analysed data are reproduced within the experimental accuracy. About 90 000 rotational and ro-vibrational transition frequencies have been computed on the basis of the spectroscopic constants obtained from the global fit in order to support data interpretation and astronomical searches in the interstellar medium and planetary atmospheres. Part of these data is included in the 2020 release of the HITRAN database.
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Thébault, P., Ammoun, M., Boudjemaa, R., Ouvrard, A., Steenkeste, K., Bourguignon, B., & Fontaine-Aupart, M. - P. (2022). Surface functionalization strategy to enhance the antibacterial effect of nisin Z peptide. Surf. Interfaces, 30, 101822.
Résumé: One of the main challenges when building antibacterial surfaces with antimicrobial peptides (AMPs) is to preserve their antimicrobial activity after stable immobilization of the peptides. Among all parameters, order/conformation of self-assembled monolayers, used as spacer, is one the most important. Herein we report the covalent immobilization of the nisin Z peptide on a gold surface functionalized with a self-assembled monolayer of 11-mercaptoundecanoic acid (MUA) alone or mixed with 6-mercaptohexanol, used as a spacer. The MUA acid is activated by treatment with carbodiimide/N-hydroxysuccinimidine and then reacts with nisin Z to form amide bonds via the N terminal part of the peptide. We have characterized each step of the surface modification using X-ray photoelectron spectroscopy, FTIR-ATR spectroscopy and contact angle measurements. The combined results show the success of each functionalization step. Additionally, SFG brings information on the orientation and conformational ordering of the self-assembled monolayers. Indeed, a better order of MUA25 layers compared to MUA was observed due to the spacing of carboxylic acid groups. The antibacterial activity of the immobilized AMPs against Staphylococcus aureus is evaluated using confocal microscopy and bacterial counting: it increases with a better order of the SAMs rather than a greater peptide concentration. This study provides fundamental insights on how to engineer AMPs and substrate to produce efficient biocidal surfaces.
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Zdanovskaia, M. A., Martin-Drumel, M. - A., Kisiel, Z., Pirali, O., Esselman, B. J., Woods, R. C., & McMahon, R. J. (2022). The eight lowest-energy vibrational states of benzonitrile: analysis of Coriolis and Darling-Dennison couplings by millimeter-wave and far-infrared spectroscopy. Journal of Molecular Spectroscopy, 383, 111568.
Résumé: A combination of millimeter-wave and high-resolution infrared data is used to analyze the eight lowest-energy vibrational states of benzonitrile (C6H5CN, C2v, μa = 4.5 D), a benzene derivative recently detected in the interstellar medium. The overtone states v22 = 2 and v33 = 2, combination state v22 = 1, v33 = 1, and fundamental states v21 = 1 and v15 = 1 are studied for the first time by rotationally resolved spectroscopy. The three former states form a Coriolis- and Darling-Dennison-coupled triad of interacting states for which the coupling terms and highly precise, deperturbed energy separations have been measured. The use of sub-millimeter and far-infrared data together enabled the determination of the purely rotational and coupling parameters for the six lowest-energy vibrationally excited states of benzonitrile, along with their highly precise energies (E22 = 141.4810252 (57) cm−1, E33 = 160.5891953 (47) cm−1, E2×22 = 282.6295417 (83) cm−1, E22+33 = 302.5795909 (87) cm−1, E2×33 = 321.4923856 (77) cm−1, E21 = 372.257993 (10) cm−1). These energies, the resultant experimental anharmonicity constants (x22,22 = − 0.1663 cm−1, x33,33 = 0.1570 cm−1, and x22,33 = 0.4909 cm−1), and semi-experimental harmonic frequencies (ω22 = 142.9 cm−1 and ω33 = 161.0 cm−1) for the ν22 and ν33 states are compared to CCSD(T)/ANO1 predicted values. The spectroscopic and coupling constants determined in this work for the vibrational ground state, the two lowest-energy fundamental states, and the corresponding first overtone and combination states successfully predict experimental frequencies down to 8 GHz. Particularly for the vibrationally excited states, the ability to predict transition frequencies so far outside the frequency region in which the constants were determined confirms that the rotational and distortion constants, as well as the coupling terms, are determined reasonably close to their true values. The ability to accurately extrapolate also demonstrates the suitability of the determined constants as the basis for extraterrestrial identification and examination of these vibrational states of benzonitrile.
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