Résumé: The Keggin-type polyoxometalate (POM) PW12O403– and the catalytic complex Cp*Rh(bpydc)Cl2 (bpydc = 2,2′-bipyridine-5,5′-dicarboxylic acid) were coimmobilized in the Zr(IV) based metal organic framework UiO-67. The POM is encapsulated within the cavities of the MOF by in situ synthesis, and then, the Rh catalytic complex is introduced by postsynthetic linker exchange. Infrared and Raman spectroscopies, 31P and 13C MAS NMR, N2 adsorption isotherms, and X-ray diffraction indicate the structural integrity of all components (POM, Rh-complex and MOF) within the composite of interest (PW12,Cp*Rh)@UiO-67. DFT calculations identified two possible locations of the POM in the octahedral cavities of the MOF: one at the center of a UiO-67 pore with the Cp*Rh complex pointing toward an empty pore and one off-centered with the Cp*Rh pointing toward the POM. 31P–1H heteronuclear (HETCOR) experiments ascertained the two environments of the POM, equally distributed, with the POM in interaction either with the Cp* fragment or with the organic linker. In addition, Pair Distribution Function (PDF) data were collected on the POM@MOF composite and provided key evidence of the structural integrity of the POM once immobilized into the MOF. The photocatalytic activity of the (PW12,Cp*Rh)@UiO-67 composite for CO2 reduction into formate and hydrogen were evaluated. The formate production was doubled when compared with that observed with the POM-free Cp*Rh@UiO-67 catalyst and reached TONs as high as 175 when prepared as thin films, showing the beneficial influence of the POM. Finally, the stability of the composite was assessed by means of recyclability tests. The combination of XRD, IR, ICP, and PDF experiments was essential in confirming the integrity of the POM, the catalyst, and the MOF after catalysis.

Résumé: Line mixing effects have been calculated in various parallel and perpendicular bands of self-broadened PH3 lines and compared with recent experimental data. The theoretical approach is an extension to symmetric tops with high inversion barrier of the formalism previously developed for NH3 [Q. Ma and C. Boulet, J. Chem. Phys. 144, 224303 (2016)]. The model takes into account the non-diagonality of the scattering operator within the line space as well as, in a correct way, the double degeneracy of the j, k levels when k ≠ 0. Transitions between such levels should be considered as doublets whose components may be coupled by the line mixing process. It has been shown that, at low pressure, the inversion of the experimental data will strongly depend on the splitting between the two components of a doublet. When it is significant, one can measure independently both the width of one component and the intra-doublet coupling matrix element. Otherwise, one can only measure the sum of these two elements. Comparisons with measurements show that the present formalism leads to accurate predictions of the experimental line shapes

Résumé: Cosmic rays (CRs) process the matter of the interstellar medium (ISM), not only modifying the interstellar matter but also injecting chemical species in the gas phase. In this work, we study the effect of CRs on astrophysical polycyclic aromatic hydrocarbons (PAHs). For events in which many electrons are stripped out from the PAHs, coulomb explosion takes place and carbon chains are produced. We computed PAH multi-ionization cross sections with a collisional model. We used another model to predict the fragmentation pattern following coulomb explosion. Experimental measurements were used to assess the validity of the calculations. The production rates of carbon chains were calculated using different CR fluxes and elemental compositions, to account for the variations expected in different astrophysical environments. PAHs with a range of sizes and levels of compactness were explored. As an average over the explored PAHs, the PAH lifetime with respect to a standard interstellar CR flux is found to be on the order of a few billion years. The production rates of chains (5–15 carbons) are slightly below the H2 ionization rate ζ. In the diffuse ISM, with 10% of the available cosmic carbon locked in PAHs, this process leads to carbon chain fractional abundances at steady state, in the range of 10−15–10−14, with a confidence interval of 1 order of magnitude. It reaches 10−13 in quiescent dense clouds. This is not sufficient to explain the observed abundances of carbon chains and complex organic molecules in dense clouds.

Résumé: Aims. Methanol ice is embedded in interstellar ice mantles present in dense molecular clouds. We aim to measure the sputtering efficiencies starting from different ice mantles of varying compositions experimentally, in order to evaluate their potential impact on astrochemical models. The sputtering yields of complex organic molecules is of particular interest, since few mechanisms are efficient enough to induce a significant feedback to the gas phase.
Methods. We irradiated ice film mixtures made of methanol and carbon dioxide of varying ratios with swift heavy ions in the electronic sputtering regime. We monitored the evolution of the infrared spectra as well as the species released to the gas phase with a mass spectrometer. Methanol (12C) and isotopically labelled 13C-methanol were used to remove any ambiguity on the measured irradiation products.
Results. The sputtering of methanol embedded in carbon dioxide ice is an efficient process leading to the ejection of intact methanol in the gas phase. We establish that when methanol is embedded in a carbon-dioxide-rich mantle exposed to cosmic rays, a significant fraction (0.2–0.3 in this work) is sputtered as intact molecules. The sputtered fraction follows the time-dependent bulk composition of the ice mantle, the latter evolving with time due to the radiolysis-induced evolution of the bulk. If methanol is embedded in a carbon dioxide ice matrix, as the analyses of the spectral shape of the CO2 bending mode observations in some lines of sight suggest, the overall methanol sputtering yield is higher than if embedded in a water ice mantle. The sputtering is increased by a factor close to the dominant ice matrix sputtering yield, which is about six times higher for pure carbon dioxide ice when compared to water ice. These experiments are further constraining the cosmic-ray-induced ice mantle sputtering mechanisms important role in the gas-phase release of complex organic molecules from the interstellar solid phase.

Résumé: Context. The UV bump observed in the interstellar medium extinction curve of galaxies has been assigned to π → π⋆ transitions within the sp2 conjugated network of carbon grains. These grains are commonly thought to be graphitic particles or polycyclic aromatic hydrocarbons. However, questions are still open regarding the shape and degree of amorphization of these particles, which could account for the variations in the 2175 Å astronomical bump. Optical spectra of graphitic and onion-like carbon structures were previously obtained from dielectric constant calculations based on oscillating dipole models. In the present study, we compute the optical spectra of entire populations of carbon clusters using an explicit quantum description of their electronic structure for each individual isomer.
Aims. Our aim is to determine the optical spectra of pure carbon clusters Cn=24,42,60 sorted into structural populations according to specific order parameters, namely asphericity and sp2 fraction, and to correlate these order parameters to the spectral features of the band in the region of the UV bump. Our comparison involves data measured for the astronomical UV bump as well as experimental spectra of carbon species formed in laboratory flames.
Methods. The individual spectrum of each isomer is determined using the time-dependent density functional tight-binding method. The final spectrum for a given population is obtained by averaging the individual spectra for all isomers of a given family. Our method allows for an explicit description of particle shape, as well as structural and electronic disorder with respect to purely graphitic structures.
Results. The spectra of the four main populations of cages, flakes, pretzels, and branched structures (Dubosq et al. 2019, A&A, 625, L11) all display strong absorption in the 2–8 eV domain, mainly due to π → π⋆ transitions. The absorption features, however, differ from one family to another and our quantum modeling indicates that the best candidates for the interstellar UV bump at 217.5 nm are cages and then flakes, while the opposite trend is found for the carbonaceous species formed in flame experiments; the other two families of pretzels and branched structures play a lesser role in both cases.
Conclusions. Our quantum modeling shows the potential contribution of carbon clusters with a high fraction of conjugated sp2 atoms to the astronomical UV bump and to the spectrum of carbonaceous species formed in flames. While astronomical spectra are better accounted for using rather spherical isomers such as cages, planar flake structures are involved as a much greater component in flame experiments. Interestingly, these flake isomers have been proposed as likely intermediates in the formation mechanisms leading to buckminsterfullerene, which was recently detected in space. This study, although restricted here to the case of pure carbon clusters, will be extended towards several directions of astronomical relevance. In particular, the ability of the present approach to deal with large-scale molecular systems at an explicit quantum level of electronic structure and its transferable character towards different charge states and the possible presence of heteroatoms makes it the method of choice to address the important case of neutral and ionic hydrogenated compounds.

Résumé: The photoelectron spectroscopy of CH2NC (isocyanomethyl) radical species is investigated for the first time between 9.3 and 11.2 eV in the vicinity of the first photoionizing transition X+1A1 ← X 2B1. The experiment combines a microwave discharge flow-tube reactor to produce the radicals through the CH3NC + F → CH2NC + HF reaction, a VUV synchrotron radiation excitation, and a double imaging electron/ion coincidence spectrometer which allows the recording of mass-selected threshold photoelectron spectra. Assignment of the observed vibrational structure of the CH2NC+ cation is guided by ab initio calculations and Franck–Condon simulations. From the experimental spectrum, the first adiabatic ionization energy of the CH2NC radical is measured as 9.439(6) eV. Fundamental wavenumbers are determined for several vibrational modes of the cation: 1+(CH2 symmetric stretch) = 2999(80) cm−1, 2+(NC stretch) = 1925(40) cm−1, 4+(H2C–N stretch) = 1193(40) cm−1, 6+(CNC out-of-plane bend) = 237(50) cm−1, and 8+(CH2 rock) = 1185(60) cm−1.

Résumé: Polycyclic Aromatic Compounds (PACs) constitute an important class of molecules found in various environments and considered as important pollutants of the earth atmosphere. In particular, functionalization of PACs modify the ring aromaticity which greatly influence the chemical reactivity of these species. In this work we studied several oxygen-containing PACs, relevant to atmospheric chemistry. We investigated the conformational landscape of four naphthalene-derivative molecules --- namely 1- and 2-hydroxynaphthalene, and 1- and 2-naphthaldehyde --- by means of rotational and vibrational spectroscopy supported by quantum chemical calculations. For 1-hydroxynaphthalene and 1-naphthaldehyde, intramolecular hydrogen bonding and steric effects drive the conformational preferences while for 2-hydroxynaphthalene and 2-naphthaldehyde, the charge distributions allow to understand the conformational landscape. This work not only demonstrates how the localization of the substitution group in the ring influences the conformational relative energies and but also constitutes a step toward a better understanding of the different chemical reactivity of such functionalized PACs.

Résumé: The C2 carbon cluster is found in a large variety of environments including flames, electric discharges, and astrophysical media. Due to spin-selection rules, assessing a complete overview of the dense vibronic landscape of the C2+ cation starting from the ground electronic state X 1Σg+ of the neutral is not possible, especially since the C2^+ ground state is of X+ 4Σg− symmetry. In this work, a flow-tube reactor source is employed to generate the neutral C2 in a mixture of both the lowest singlet X 1Σg+ and triplet a 3Πu electronic states. We have investigated the vibronic transitions in the vicinity of the first adiabatic ionization potential via one-photon ionization with vacuum ultraviolet synchrotron radiation coupled with electron/ion double imaging techniques. Using ab initio calculations and Franck-Condon simulations, three electronic transitions are identified and their adiabatic ionization energy is determined Ei(a+2Πu←X1Σ+g)=12.440(10) eV, Ei(X+4Σ−g←a3Πu)=11.795(10) eV, and Ei(a+2Πu ← a3Πu) = 12.361(10) eV. From the three origin bands, the following energy differences are extracted: ΔE(a − X) = 0.079(10) eV and ΔE(a+ − X+) = 0.567(10) eV. The adiabatic ionization potential corresponding to the forbidden one-photon transition X+ ← X is derived and amounts to 11.873(10) eV, in very good agreement with the most recent measurement by Krechkivska et al. [J. Chem. Phys. 144, 144305 (2016)]. The enthalpy of formation of the doublet ground state C2^+ cation in the gas phase is determined at 0 K, ΔfH0(0K)(C+2(Πu2))=2019.9(10) kJ mol−1. In addition, we report the first experimental ion yield of C2 for which only a simple estimate was used up to now in the photochemistry models of astrophysical media due to the lack of experimental data.

Résumé: We show that the decays with pressure of the rotational alignment echoes induced in
N
2
O
-He gas mixtures by two ultrashort laser pulses with various delays show detailed information about collision-induced changes of the rotational speed of the molecules. Measurements and classical calculations consistently demonstrate that collisions reduce the echo amplitude all the more efficiently when the echo appears late. We quantitatively explain this behavior by the filamentation of the classical rotational phase space induced by the first pulse and the narrowing of the filaments with time. The above-mentioned variation of the echo decay then reflects the ability of collisions to change the molecular rotation speed by various amounts, enabling refined tests of models for the dissipation induced by intermolecular forces. We also demonstrate that the collision-induced changes of the rotational speed within the filaments are the classical equivalents of the nonsecular transfers among quantum coherences, thus evidencing the correspondence between the classical and quantum worlds.

Résumé: A double-imaging photoelectron-photoion spectrometer and synchrotron radiation have been used to measure the HBr+ X 2Π3/2 v+ = 0, 1, 2 and the 2Π1/2 v+ = 0 state photoelectron angular distributions, as characterized by the anisotropy parameter β, the total ion yield, and the threshold photoelectron spectrum. Particular attention has been focussed on the photon energy range between the 2Π3/2 and the 2Π1/2 spin–orbit components of the ground ionic state. This region encompasses Rydberg states, belonging to series converging onto the upper 2Π1/2 ionization limit, which may decay by autoionization into the 2Π3/2 ionization continuum. A detailed study has been performed on the effects of autoionization on the 2Π3/2 v+ = 0 state photoelectron angular distributions. The observed energy dependent variations in the β-values exhibit a regular pattern that correlates with excitation into members of a very broad d-type Rydberg series. Additional rapid variations in the β-parameters, which occur over a narrow energy range, appear to coincide with sharp autoionizing Rydberg states belonging to s, p and d series. The present experimental results for the HBr+ X 2Π3/2 v+ = 0 state photoelectron anisotropy parameter are compared to previously reported theoretical predictions and to earlier studies of the Kr+ 4p5 2P3/2 state β-parameter. The threshold photoelectron spectrum of the X 2Π3/2 v+ = 0 band exhibits partially resolved rotational structure. A simulation of this structure yields an ionization threshold of 11.6673 ± 0.0010 eV, which is consistent with previous measurements.

Résumé: The high resolution far-infrared spectrum of trans-butadiene has been re-investigated by Fourier-transform spectroscopy at two synchrotron radiation facilities, SOLEIL and the Canadian Light Source, at temperatures ranging from 50 to 340 K. Beyond the well-studied bands, two new fundamental bands lying below 1100 cm-1, ν10 and ν24, have been assigned using a combination of cross-correlation (ASAP software) and Loomis-Wood type (LWWa software) diagrams. While the ν24 analysis was rather straightforward, ν10 exhibits obvious signs of a strong perturbation, presumably owing to interaction with the dark ν9+ν12 state. Effective rotational constants have been derived for both the v10 = 1 and v24 = 1 states. Since only one weak, infrared active fundamental band (ν23) of trans-butadiene remains to be observed at high resolution in the far-infrared, searches for the elusive gauche conformer can now be undertaken with considerably greater confidence in the dense ro-vibrational spectrum of the trans form.

Résumé: Cyanoacetylene, the simplest cyanopolyyne, is an abundant interstellar molecule commonly observed in a vast variety of astronomical sources. Despite its importance as a potential tracer of the evolution of star-forming processes, the deuterated form of cyanoacetylene is less observed and less studied in the laboratory than the main isotopologue. Here, we report the most extensive spectroscopic characterization of DC3N to date, from the millimeter domain to the infrared region. Rotational and ro-vibrational spectra have been recorded using millimeter-wave frequency-modulation and Fourier-transform infrared spectrometers, respectively. All the vibrational states with energy up to 1015 cm−1 have been analyzed in a combined fit, where the effects due to anharmonic resonances have been adequately accounted for. The analysis contains over 6500 distinct transition frequencies, from which all the vibrational energies have been determined with good precision for many fundamental, overtone, and combination states. This work provides a comprehensive line catalog for astronomical observations of DC3N.

Résumé: The sum-of-products finite-basis-representation (SOP-FBR) approach for the automated multidimensional fit of potential energy surfaces (PESs) is presented. In its current implementation, the method yields a PES in the so-called Tucker sum-of-products form, but it is not restricted to this specific ansatz. The novelty of our algorithm lies in the fact that the fit is performed in terms of a direct product of a Schmidt basis, also known as natural potentials. These encode in a non-trivial way all the physics of the problem and, hence, circumvent the usual extra ad hoc and a posteriori adjustments (e.g., damping functions) of the fitted PES. Moreover, we avoid the intermediate refitting stage common to other tensor-decomposition methods, typically used in the context of nuclear quantum dynamics. The resulting SOP-FBR PES is analytical and differentiable ad infinitum. Our ansatz is fully general and can be used in combination with most (molecular) dynamics codes. In particular, it has been interfaced and extensively tested with the Heidelberg implementation of the multiconfiguration time-dependent Hartree quantum dynamical software package.

Résumé: Diffusion is an important process for molecular transport inside plant cells. Recent advancement in plant physiological study demands verification of the diffusion process at the single cell level. In this work, the real-time intracellular diffusion of nanoparticles in the cytoplasm of single plant cells was realized using photoinjection with femtosecond laser amplifier. The diffusion behavior was analyzed by estimating the diffusion coefficient in cytoplasm. In addition, the effect of particle size to the photoinjection efficiency and diffusion was evaluated. Surprisingly, the intercellular diffusion of nanoparticles between single plant cells was also directly observed.

Résumé: Novel fluorescent labels with high photostability and high biocompatibility are required for microbiological imaging and detection. Here, we present a green fluorescent polymer chain (GFPC), designed to be nontoxic and water-soluble, for multicolor bioimaging and real-time bacterial viability determination. The copolymer is synthesized using a straightforward one-pot reversible addition–fragmentation chain-transfer (RAFT) polymerization technique. We show that GFPC does not influence bacterial growth and is stable for several hours in a complex growth medium and in the presence of bacteria. GFPC allows the labeling of the bacterial cytoplasm for multicolor bacterial bioimaging applications. It can be used in combination with propidium iodide (PI) to develop a rapid and reliable protocol to distinguish and quantify, in real time, by flow cytometry, live and dead bacteria.

Résumé: We investigate spin-orbit interactions in ultrafast molecular processes employing the exact factorization of the electron-nuclear wave function. We revisit the original derivation by including spin-orbit coupling, and show how the dynamics driven by the time-dependent potential energy surface alleviates inconsistencies arising from different electronic representations. We propose a novel trajectory-based scheme to simulate spin-forbidden non-radiative processes, and we show its performance in the treatment of excited-state dynamics where spin-orbit effects couple different spin multiplets.

Résumé: Reducing atmospheres have recently emerged as a promising scenario to warm the surface of early Mars enough to drive the formation of valley networks and other ancient aqueous features that have been detected so far on the surface of Mars. Here we present a series of experiments and calculations to better constrain CO2 + CH4 and CO2 + H2 collision-induced absorptions (CIAs) as well as their effect on the prediction of early Mars surface temperature. First, we carried out a new set of experimental measurements (using the AILES line of the SOLEIL synchrotron) of both CO2 + CH4 and CO2 + H2 CIAs. These measurements confirm the previous results of Turbet et al. (2019), Icarus vol. 321, while significantly reducing the experimental uncertainties. Secondly, we fitted a semi-empirical model to these CIAs measurements, allowing us to compute the CO2 + CH4 and CO2 + H2 CIAs across a broad spectral domain (0–1500 cm−1) and for a wide range of temperatures (100–600 K). Last, we performed 1-D numerical radiative-convective climate calculations (using the LMD Generic Model) to compute the surface temperature expected on the surface of early Mars for several CO2, CH4 and H2 atmospheric contents, taking into account the radiative effect of these revised CIAs. These calculations demonstrate that thick CO2 + H2-dominated atmospheres remain a viable solution for warming the surface of Mars above the melting point of water, but not CO2 + CH4-dominated atmospheres. Our calculated CO2 + CH4 and CO2 + H2 CIA spectra and predicted early Mars surface temperatures are provided to the community for future uses.