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Dicarboxylic acids are an essential component of tropospheric aerosols emitted directly or formed in chemical processes. The physiochemical properties and heterogeneous oxidation of aerosol particles containing maleic acid (MA) have been investigated using a mixed quantum and classical approach. The multiphase reactions of primary ozonide formation between the gas phase, the particle interface, and its bulk strongly influence the reaction mechanism and rate coefficients. Based on snapshots issued taken from molecular dynamics simulations, the mechanism of MA + O3 reaction is investigated in three different environments using ab initio method and density functional theory. The interfacial water molecules enhance the initial reaction step of MA + O3, with a larger rate constant at the air-water interface than in the gas phase. By assuming the Langmuir-Hinshelwood behavior and comparing it with the bulk, the ozonolysis of maleic acid mainly occurs in the bulk, and O3 diffusion in the bulk may be the limiting process.

Oceans, through algae and phytoplankton activities, are the main source of iodine, including monohalogenated organic compounds as CH3I [1]. There is missing knowledge about interactions between iodinated compounds and aerosols in the troposphere. In this context, this work investigates the adsorption of gaseous iodomethane (CH3I) on model sea-salt aerosols at various humidities. The water coverage tends to stabilize CH3I at the salt surface. The lifetime of CH3I in the atmosphere (in gas phase or adsorbed on aerosols) may be altered by its reaction with gas phase radicals. The reaction of CH3I with OH is thus investigated both in gas phase and in presence of water by means of quantum mechanical calculations. References:[1] Saiz-Lopez et al, Chem. Rev. 2012, 112, 1773–1804. Acknowledgments: I-SITE ULNE OVERSEE project (contract ANR-16-IDEX-004)The CaPPA project (Chemical and Physical Properties of the Atmosphere) is funded by the French National Research Agency (ANR) through the PIA (Programme d’Investissement d’Avenir) under contract « ANR-11-LABX-0005-01 » and by the Regional Council « Hauts-de-France » and the « European Funds for Regional Economic Development » (FEDER)

International audience; Aerosol particles are known to have a major impact on the climate by directly absorbing and scattering solar radiation and indirectly by acting as cloud condensation nuclei. The main contribution to aerosol emission comes from the ocean through the production of sea spray aerosols (SSA), which consist of organic and inorganic species, formed in different sizes and shapes, depending on their mixing ratios. The chemical composition of those SSA will be naturally impacted by the chemical composition of the air/water interface. Through complex experiments, it has been shown how surface activity impacts the selective transfer of species from solution to the aerosol phase. While experiments offer a general picture, it is interesting to probe the properties through a systematic and decoupled approach at the molecular level. The present study provides indeed theoretical results to be confronted to reported experimental observations by means of molecular level simulations. We chose a series of linear mono- and dicarboxylates (containing 4, 6, or 8 carbon atoms) being identified as a large fraction of the SSA surface composition, with the possible counterions (Na+, K+, Ca2+, Mg2+). Classical molecular dynamics is employed to model the distribution of these ions in a water slab using an ab initio based polarizable force-field model. These calculations allow us to derive some trends on the enrichment of inorganic and organic ions at the liquid–air interface compared to their eventual partitioning in the bulk phase. Indeed, medium to long chain mono- or dicarboxylates predominantly remain at the surface of the aerosol, with inorganic cations accumulating underneath, neutralizing the surface charge. For shorter chains, solvation in the bulk appears more favorable. K+ and the dications show a strong ion pairing with the organics, this ion pairing driving their surface vs bulk distribution. In addition, surface tension has been evaluated for the long chain, i.e., having 8 carbons, mono- and dicarboxylates in the presence of the various cations. The surface propensity of the organic chains leads in general to a reduction of surface tension compared to neat water, while mixtures of dicarboxylates and dications give higher values. Finally, these outcomes are discussed in comparison with previous work and within the context of SSA chemistry.

National audience; Iodine-131 can be released during a severe nuclear accident and can be carcinogenic for humans [1]. In the literature, there are missing pieces of knowledge about inter-actions between iodinated compounds and aerosols in the troposhere. In this context,this work consists in investigating the adsorption on sea salt aerosols and ice of gaseous iodomethane (CH2I). A force field has been parametrized and used in classical molecular dynamics calculations. This method allows to sample large systems and a wide range ofconfigurations. These configurations serve as starting geometries in a QM/QM’ ONIOM [2, 3] approach to compute the IR frequencies. In addition, periodic ab initio calculationshave been carried out [4, 5]. Adsorption energies and vibrational frequency shifts upon adsorption are thus quantified. We show that the vibrational frequency shifts are small, mainly because there is no strong coupling between the adsorbates and the surfaces. We also illustrate the differences on the adsorption between the crystal and amorphous ice at low temperature.[1] Dobyns, B. M.; Sheline, G. E.; Workman, J. B.; Tompkins, E. A.; McConahey, W. M.; Becker,D. V.J. Clin. Endocrinol. Metab., 38, 976–998 (1974)[2] Svensson, M.; Humbel, S.; Froese, R. D.; Matsubara, T.; Sieber, S.; Morokuma, K.J. Phys. Chem.,100, 19357–19363 (1996)[3] Frisch, M. J. et al. Gaussian 16 Revision B.01, Gaussian Inc. Wallingford CT (2016) [4] Giannozzi, P. et al.J. Phys. Condens. Matter, 21, 395502 (2009)[5] Giannozzi, P. et al.J. Phys. Condens. Matter,29, 465901 (2017)Acknowledgements:PIA MiRE(ANR-11-LABX-0005-01)I-SITE ULNE OVERSEE project (contract ANR-16-IDEX-004)

We investigate for the first time the gas-phase lowest-lying valence, Rydberg and ionic electronic states of 2,4,6-trichloroanisole (TCA) using synchrotron radiation for photoabsorption and photoelectron spectroscopy. The high-resolution vacuum ultraviolet photoabsorption spectrum, in the 4.0-10.8 eV energy-range, has been measured with absolute photoabsorption cross-sections and, thanks to novel ab initio calculations of the vertical energies and oscillator strengths, an assignment of the electronic transitions is comprehensively reported. The assignment of weak vibrational features in the absorption bands of TCA reveal that the ring and C-Cl stretching modes are mainly active. In the photoelectron spectrum the lowest 18 ionic bands, between 8 and 30 eV, have been observed and assigned using the first set of calculated valence and outer valence vertical ionisation energies. Finally, the measured absolute photoabsorption cross sections have also been used to estimate the photolysis lifetime of TCA in the upper stratosphere (20-50 km). Crown Copyright (C) 2021 Published by Elsevier Ltd. All rights reserved.

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The growth of small valeric (pentanoic) and glutaric (pentanedioic) acid aerosol particles from 20 to 500 molecules has been investigated at room temperature using classical molecular dynamics simu...

Photoabsorption spectra of isoflurane and sevoflurane have been measured with synchrotron radiation over the photon range 5.0–10.8 eV. Low-lying excited singlet valence and Rydberg states are investigated and the assignments supported by quantum chemical calculations, the latter also helping to identify the triplet states. This provides the first comprehensive investigation of all excited electronic states up to the first ionisation energy. The Rydberg series converging to the ionisation energy limits are identified according to the magnitude of the quantum defects. The measured absolute cross-sections have been used to calculate the photolysis lifetimes of isoflurane and sevoflurane in the Earth’s atmosphere.

The uptake of atmospheric gaseous oxidant such as O3 or the ROx (OH, HO2, RO2) family, have a strong impact on the oxidative capacity of the atmosphere. [1], [2] Last decade, few studies have been carried out on the uptake of such compounds on atmospheric aerosol. However, the large variety of organic compounds provides uptake coefficients with a wide range of order of magnitude. [3], [4] Furthermore, the uptake resulting from the combination of different processes (mass accommodation, bulk diffusion, reactivity), the detailed understanding of such a process is not always accessible through experiments. Theoretical tools such as quantum mechanics (QM) combined with Molecular Mechanics (MM) is one way to investigate separately the different processes.The ONIOM hybrid QM/MM method [5] allows to study the reactivity of few molecules in a large system. In our group, a methodology using this computational method have been developed in order to estimate the reactive uptake of gaseous compounds onto organic aerosol particles. In this presentation, reactive uptake of HO2 and O3 onto glutaric acid and oleic acid aerosols respectively will be discussed. Comparisons will be addressed with gas phase theoretical reaction rates and with experimental data.We acknowledge support by the French government through the Program “Investissement d'avenir” through the Labex CaPPA (contract ANR-11-LABX-0005-01) and I-SITE ULNE project OVERSEE (contract ANR-16-IDEX-0004), CPER CLIMIBIO (European Regional Development Fund, Hauts de France council, French Ministry of Higher Education and Research) and French national supercomputing facilities (grants DARI x2016081859 and A0050801859). References[1] H. L. Macintyre and M. J. Evans, “Parameterisation and impact of aerosol uptake of HO2 on a global tropospheric model,” Atmos. Chem. Phys., vol. 11, no. 21, pp. 10965–10974, Nov. 2011, doi: 10.5194/acp-11-10965-2011.[2] M. Zeng and K. R. Wilson, “Efficient Coupling of Reaction Pathways of Criegee Intermediates and Free Radicals in the Heterogeneous Ozonolysis of Alkenes,” The Journal of Physical Chemistry Letters, Jul. 2020, doi: 10.1021/acs.jpclett.0c01823.[3] P. S. J. Lakey, I. J. George, L. K. Whalley, M. T. Baeza-Romero, and D. E. Heard, “Measurements of the HO2 Uptake Coefficients onto Single Component Organic Aerosols,” Environ. Sci. Technol., vol. 49, no. 8, pp. 4878–4885, Apr. 2015, doi: 10.1021/acs.est.5b00948.[4] M. Mendez, N. Visez, S. Gosselin, V. Crenn, V. Riffault, and D. Petitprez, “Reactive and Nonreactive Ozone Uptake during Aging of Oleic Acid Particles,” J. Phys. Chem. A, vol. 118, no. 40, pp. 9471–9481, Oct. 2014, doi: 10.1021/jp503572c.[5] L. W. Chung et al., “The ONIOM Method and Its Applications,” Chem. Rev., vol. 115, no. 12, pp. 5678–5796, Jun. 2015, doi: 10.1021/cr5004419.

International audience; Iodine, when released into the environment, contributes to the oxidizing capacity of the atmosphere through the catalytic destruction of ozone [1, 2]. Iodine-131 can be released during a severe nuclear accident and can be carcinogenic for humans [3]. In the literature, there are missing pieces of knowledge about interactions between iodinated compounds and aerosols. In this context, this work consists in investigating the adsorption on sea salt aerosols of gaseous methyl iodide (CH3I), diiodomethane (CH2I2), and water. We have used two different methods: a periodic approach using Quantum ESPRESSO [4, 5] and a cluster QM/QM' approach using the ONIOM method [6] from Gaussian 16 [7]. We have computed the adsorption energies and the shift in vibrational frequencies, due to adsorption. We have shown that the vibrational frequency shifts are small, mainly because there is no strong coupling between the adsorbates and the NaCl (001) surface, as illustrated by the low values of the adsorption energies.(1) Saiz-Lopez, A.; Plane, J. M. C.; Baker, A. R.; Carpenter, L. J.; von Glasow, R.; Gómez Martín, J. C.; McFiggans, G.; Saunders, R. W. Chem. Rev. 2012, 112, 1773-1804(2) Calvert, J. G.; Lindberg, S. E. Atmospheric Environ. 2004, 38, 5087-5104(3) Dobyns, B. M.; Sheline, G. E.; Workman, J. B.; Tompkins, E. A.; McConahey, W. M.; Becker, D. V. J. Clin. Endocrinol. Metab. 1974, 38, 976(4) Giannozzi, P. et al. J. Phys. Condens. Matter 2009, 21, 395502(5) Giannozzi, P. et al. J. Phys. Condens. Matter 2017, 29, 465901(6) Svensson, M.; Humbel, S.; Froese, R. D.; Matsubara, T.; Sieber, S.; Morokuma, K. J. Phys. Chem. 1996, 100, 19357-19363(7) Frisch, M. J. et al. Gaussian 16 Revision B.01, Gaussian Inc. Wallingford CT, 2016

No. 2019-A0010806820 UIDB/00068/2020 PTDC/FIS-AQM/31281/2017 Abstract: We present novel results of the analysis of the electronic structure of two aliphatic esters: methyl butyrate and methyl valerate. High-resolution photoabsorption spectra were collected and analyzed over the energy range 4.0–10.8 eV and showed for both the molecules not only a clear band of the HOMO to LUMO transition, but also vibronic structure associated with the first Rydberg-valence transition. Photoelectron spectra recorded from 9 to over 28 eV revealed many ionization states with the first adiabatic ionization energies found to be 9.977 eV and 9.959 eV for methyl butyrate and methyl valerate, respectively. Ab initio calculations have been performed in order to help assign the photoabsorption and photoelectron features. Photolysis life times in the atmosphere were calculated revealing that photolysis is not competitive over hydroxyl radical scavenging in the process of removal of these esters from the atmosphere. Graphical abstract: [Figure not available: see fulltext.] publishersversion published

International audience; We present a comprehensive experimental high-resolution vacuum ultraviolet (VUV) photoabsorption spectrum of dichloromethane, CH2Cl2, with absolute cross sections determined for the full 5.8–10.8 eV energy-range. The calculations on the vertical excitation energies and oscillator strengths were performed using the equation-of-motion coupled cluster method, restricted to the single and double excitations level (EOM-CCSD), and were used to help analyse the valence and Rydberg structures in the photoabsorption spectrum. The present spectrum additionally reveals several new features not previously reported in the literature, with particular reference to the valence σ*CCl (10a1) ← nCl (7b2) (11B2 ← X1A1) and (σ*CCl (10a1) ← nCl (9a1) + σ*CH (11a1) ← nCl (7b2)) (11A1 ← X 1A1) transitions at 7.519 and 7.793 eV. A vibrational progression of the CCl2 symmetric stretching, ν'3, and CCl2 scissoring, ν'4 (a1), modes have also been assigned for the first time in the 7.4–8.6 eV energy range. The measured absolute photoabsorption cross sections have been used to calculate the photolysis lifetime of dichloromethane in the Earth's atmosphere (0–50 km). Potential energy curves as a function of the C–Cl coordinate, for the four lowest-lying excited A′ and A″ electronic states, have additionally been calculated at the EOM-CCSD level of theory.

Significant uncertainties are still associated to chemical reaction mechanisms used in atmospheric models, in particular for ROx radicals (OH, HO2, RO2). Recent measurements of radicals in forested areas characterized by low NOx (NO2, NO) concentrations indicate that models can significantly overestimate peroxy radical concentrations.1,2 These results question the ability of models to correctly simulate the oxidative capacity of the troposphere since peroxy radicals are a main source of the hydroxyl radical (OH), one of the most important oxidative species in the atmosphere.3 One possible explanation is the occurrence of heterogeneous processes (uptake of radicals) on the surface of aerosols that are either misrepresented or not included in models. While recent studies have reported uptake coefficients of HO2 on different types of aerosols, the process is not completely understood yet.Molecular dynamics combined with ab-initio calculations have been used to study HO2 reactive uptake on organic aerosols. The sticking process of HO2 and its reactivity have been modelled on a nanometer size aerosol particle.4 Those theoretical calculations provide insight into the uptake process at the molecular scale and are planned to be compared to experimental measurements carried out with an aerosol flow tube.This work is supported by the CaPPA project (Chemical and Physical Properties of the Atmosphere), funded by the French National Research Agency (ANR) through the PIA (Programme d’investissement d’avenir) and by the regional council “Hauts-de-France”. The authors also thank CPER Climibio and FEDER for their financial support. Calculations were performed using HPC resources from GENCI-TGCC (Grant 2020- A0070801859).References[1] T. Griffith et al., Atmos. Chem. Phys. 13, 5403 (2013) [2] Mao et al., Atmos. Chem. Phys. 12, 8009 (2012) [3] Stone et al., Chem. Soc. Rev. 41, 6348 (2012) [4] Roose et al., ACS Earth Space Chem. 3, 380 (2019)

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We present a comprehensive revisited experimental high-resolution vacuum ultraviolet (VUV) photoabsorption spectrum of ammonia, NH, covering for the first time the full 5.4-10.8 eV energy-range, with absolute cross sections determined. The calculations on the vertical excitation energies and oscillator strengths were performed using the equation-of-motion coupled cluster method restricted to single and double excitation levels and used to help reanalyze the observed Rydberg structures in the photoabsorption spectrum. The VUV spectrum reveals several new features that are not previously reported in the literature, with particular reference to the vibrational progressions of the (D'1EX'1A1′), the (F'1EX'1A1′), and the (G'1A2X'1A1′) absorption bands. In addition, new Rydberg members have been identified in nda11a2″D'′′1A2X'1A1′, where n > 3 has not been reported before as well as in nde1a2″F'1EX'1A1′ and in nsa1 1a2″G'1A2X'1A1′. The measured absolute photoabsorption cross sections have been used to calculate the photolysis lifetime of ammonia in the Earth's atmosphere (0-50 km)., M.M. and F.F.S. acknowledge the Portuguese National Funding Agency FCT-MCTES through Grant No. PD/BD/106038/2015 and researcher position IF-FCT IF/00380/2014, respectively, and together with A.I.L. and P.L.-V. the research Grant Nos. UID/FIS/00068/2019 (CEFITEC), PTDC/FIS-AQM/31281/2017, and PTDC/FIS-AQM/31215/2017. This work was also supported by Radiation Biology and Biophysics Doctoral Training Programme (RaBBiT, Grant No. PD/00193/2012) and Grant No. UID/Multi/04378/2013 (UCIBIO). P.L.-V. also acknowledges his visiting professor position at Sophia University, Tokyo, Japan. The authors wish to acknowledge the beam time at the ISA synchrotron radiation source ASTRID2, Aarhus University, Denmark. D.D. acknowledges the support of the grants OVERSEE and CAPPA, managed by the Agence Nationale de la Recherche, Contract Numbers ANR-16-IDEX-0004 ULNE (I-SITE ULNE) and ANR-10-LABX-005 (CAPPA). D.D. also thanks the Région Hauts de France, the Ministère de l’Enseignement Supérieur et de la Recherche (CPER Climibio), and the European Fund for Regional Economic Development for their support. This work used HPC resources from GENCI-TGCC (Grant No. 2019-A0010806820) and the Centre de Ressources Informatiques (CRI) of the Université de Lille. G.G. acknowledges partial support from the Spanish Ministerio de Ciencia, Innovación y Universidades (Project No. FIS2016-80440) and CSIC (Project No. LINKA20085). This work was conducted under the support of the Ministry of Education, Culture, Sport, Science and Technology (MEXT), Japan.

International audience; Significant uncertainties are still associated to chemical reaction mechanisms used in atmospheric models, in particular for ROx radicals (OH, HO2, RO2). Recent measurements of radicals in forested areas characterized by low NOx (NO2, NO) concentrations indicate that models can significantly overestimate peroxy radical concentrations.1,2 These results question the ability of models to correctly simulate the oxidative capacity of the troposphere since peroxy radicals are a main source of the hydroxyl radical (OH), one of the most important oxidative species in the atmosphere.3 One possible explanation is the occurrence of heterogeneous processes (uptake of radicals) on the surface of aerosols that are either misrepresented or not included in models. While recent studies have reported uptake coefficients of HO2 on different types of aerosols, uptakes of RO2 radicals have yet to be investigated and the process is not completely understood yet.Both theoretical and experimental tools have been used to study HO2 uptake on organic aerosols. A PERCA (Peroxy Radical Chemical Amplifier) instrument capable of measuring HO2 and RO2 radical concentrations has been coupled to an aerosol flow tube to quantify HO2 uptakes on glutaric acid aerosols at different relative humidities. In complement to this experimental work, molecular dynamics combined with ab-initio calculations has been used to model a nanometer size aerosol particle and the sticking process of HO2 on the organic particle. These theoretical calculations provide insight into the uptake process at the molecular scale. In this presentation, we will emphasize the advantage of using a dual experimental/theoretical approach to investigate the uptake of radical species on atmospheric aerosols.This work is supported by the CaPPA project (Chemical and Physical Properties of the Atmosphere), funded by the French National Research Agency (ANR) through the PIA (Programme d’investissement d’avenir) and by the regional council “Hauts-de-France”. The authors also thank CPER Climibio and FEDER for their financial support. Calculations were performed using HPC resources from GENCI-TGCC (Grant 2017-A0010806820).References[1] P. T. Griffith et al., Atmos. Chem. Phys. 13, 5403 (2013) [2] J. Mao et al., Atmos. Chem. Phys. 12, 8009 (2012)[3] D. Stone et al., Chem. Soc. Rev. 41, 6348 (2012)

The emission and use of synchrotron radiation (SR) are powerful tools for performing state-of-the art research at the fundamental and applied levels, benefiting a diversity of research areas across medicine, molecular and cell biology, condensed matter physics, nanotechnology, cultural heritage, environmental science, atomic and molecular physics, among many others.

International audience; Perfluorocarbons, a class of fully fluorinated compounds, are highly persistent and toxic pollutants that are receiving increasing attention due to their widespread environmental distribution. In this study, attention was focused on one compound in particular, namely, perfluorooctanoic acid (PFOA). The first investigation of the UV/VUV photochemistry of the PFOA anion in the gas phase by action spectroscopy of selected ions is reported. Two main relaxation channels were identified: photodissociation and photodetachment. Absolute cross sections for the individual observed processes were measured. DFT calculations and natural transition orbital analysis were carried out to help in the interpretation of the experimental results.

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International audience; Carotenoids are important natural pigments and micronutrients contributing to health prevention by several mechanisms, including their electron-donating (antioxidant) activity. In this work, a large series of carotenoids, including 11 carotenes and 14 xanthophylls, have been investigated by wavelength-resolved atmospheric pressure photoionization mass spectrometry (DISCO line of SOLEIL synchrotron), thus allowing the experimental determination of their ionization energy (IE) for the first time. On the other hand, the carotenoids have been also investigated for their ability to inhibit the heme iron-induced peroxidation of linoleic acid in mildly acidic micelles, a simple but relevant chemical model of oxidative stress in the gastric compartment. Thus, the carotenoids can be easily classified from IC50 concentrations deduced from the time dependence of the lipid hydroperoxide concentration. With a selection of two carotenes and three xanthophylls a quantitative analysis is also provided to extract stoichio-kinetic parameters. The influence of the carotenoid structure (number of conjugated carbon−carbon double bonds, presence of terminal six-membered rings, hydroxyl, keto, and/or epoxy groups) on the IE, IC50, and stoichio-kinetic parameters is discussed in details. The data show that the antioxidant activity of carotenes is well correlated to their electron-donating capacity, which itself largely depends on the length of the conjugated polyene chain. By contrast, the IE of xanthophylls is poorly correlated to the polyene chain length because of the strong, and sometimes unexpected, electronic effects of the O-atoms. Although IE remains an approximate predictor of the antioxidant activity of xanthophylls, other factors (interaction with the aqueous phase, competing radical-scavenging mechanisms, the residual activity of the antioxidant’s oxidation products) probably play a significant role.

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Electron energy loss spectra of carbon tetrafluoride, silicon tetrafluoride, and germanium tetrafluoride molecules (CF4, SiF4, and GeF4) have been measured for incident electron energies of 50-360 eV at 1.5°-15.5° and for 30 eV and 30° scattering angle, while sweeping the energy loss over the range 9.0-20.0 eV. Low-lying valence excited triplet and singlet states are investigated by quantum chemical ab initio calculations. The Rydberg series converging to the (lowest) ionisation energy limits of XF4 (X = C, Si, Ge) are also identified and classified using the systematic behaviour according to the magnitude of the quantum defects. A generalized oscillator strength analysis is employed to derive oscillator strength f0 value and the apparent Born integral cross sections from the corresponding differential cross sections by using the Vriens formula for the optically allowed transitions. The f0 value is compared with the optical oscillator strength of the photoabsorption, pseudo-photon measurements, and theoretical values. The binary-encounter and f-scaled Born cross sections of the most intense optically allowed transitions have been also derived from the excitation threshold to the high energy region where the Born approximation is valid. Potential energy curves were obtained along the XF3 + F coordinate with two different basis sets to lend support on electron impact dissociation processes yielding radical formation. We found that in CF4, the lowest-lying dissociative character is due to intramolecular conversion from Rydberg 3s to valence character (σ*(C-F)), whereas in SiF4 and GeF4, an antibonding behaviour prevails.

Photoionization of a buckminsterfullerene ion is investigated using an ion trap and a merged beam setup coupled to synchrotron radiation beamlines and compared to theoretical calculations. Absolute measurements derived from the ion trap experiment allow discrepancies concerning the photoionization cross section of C-60(+) to be solved.

International audience; We report on measurements of integral cross sections (ICSs) for electron impact excitation of a series of Rydberg electronic-states in α-tetrahydrofurfuryl alcohol. The energy range of these experiments was 20–50 eV. There are currently no other results against which we can directly compare those measured data. We also report results from our independent atom model with screened additivity rule correction computations, namely for the total cross section, elastic ICS, inelastic ICS (all discrete electronic states and neutral dissociation) and the total ionisation ICS. Where possible, our calculated cross sections are compared to the limited available data of each scattering process.

International audience; Marine aerosols represent the most important aerosol fraction in the Earth atmosphere. Field studies have revealed that fatty acids form an organic film at the surface of sea salt particles, altering the properties of the aerosol. By means of classical molecular dynamics simulation, the surface organization of palmitic acid (PA) on a salt surface, NaCl, has been investigated at two different temperatures, 235 and 300 K, and with relative humidity varying from 0 to 40%. Calculations show that water promotes the formation of well-ordered close-packed PA islands. As a result, some area of the salt may be covered by water only or by PA molecules supported by water. Depending on the relative humidity, the hydrophilic/hydrophobic character of the sea salt surface varies. This heterogeneous coating gives rise locally to very different surface properties and hence may affect the transfer of gas phase species to the salt and their reactivity.

Electron energy loss (EEL) spectra of GeF4 have been measured with incident electrons at 100 eV for 5° scattering angle and at 30 eV for 30° scattering angle, while sweeping the energy loss over the range 7.0–18.0 eV. Low-lying excited triplet, singlet, valence, and Rydberg states are investigated and the assignments supported by quantum chemical ab initio calculations. This provides the first comprehensive investigation of all singlet and triplet excited electronic states of germanium tetrafluoride up to the first ionization energy. The Rydberg series converging to the (lowest) ionization energy limits of GeF4 are also identified according to the magnitude of the quantum defects (δ).

P.L.V. and F.F.S. acknowledge the Portuguese National Funding Agency FCT-MCTES through Grant Nos. UID/FIS/00068/2013 and IF-FCT IF/00380/2014. E.L. acknowledges the Brazilian Agency Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq) and the Science Without Borders Programme for opportunities to study abroad. D.D. acknowledges support from the CaPPA project (Chemical and Physical Properties of the Atmosphere), funded by the French National Research Agency (ANR) through the PIA (Programme d'Investissement d'Avenir) under Contract No. ANR-10-LABX-005 and by the Regional Council "Nord-Pas de Calais" and the "European Funds for Regional Economic Development" (FEDER). M.A.S. would like to acknowledge the Visiting Research Fellow position at The Open University. This work was performed using HPC resources from GENCI-CINES (Grant No. 2015-088620). The Centre de Ressources Informatiques (CRI) of the Universite of Lille also provided computing time. The authors wish to acknowledge the beam time at the ISA synchrotron at Aarhus University, Denmark. We also acknowledge the financial support provided by the European Community's Seventh Framework Programme (No. FP7/2007-2013) CALIPSO under Grant Agreement No. 312284. M.J.B. acknowledges financial support provided through the Australian Research Council (ARC). We present the experimental high-resolution vacuum ultraviolet (VUV) photoabsorption spectra of phenol covering for the first time the full 4.3-10.8 eV energy-range, with absolute cross sections determined. Theoretical calculations on the vertical excitation energies and oscillator strengths were performed using time-dependent density functional theory and the equation-of-motion coupled cluster method restricted to single and double excitations level. These have been used in the assignment of valence and Rydberg transitions of the phenol molecule. The VUV spectrum reveals several new features not previously reported in the literature, with particular reference to the 6.401 eV transition, which is here assigned to the 3s sigma/sigma*(OH) publishersversion published

International audience; In the nitrosyl halides series (XNO, where X = F, Cl, Br, I), INO is the only chemical species whose rotational spectrum has not been reported. Nitrosyl iodide, together with the nitryl (INO2), nitrite (IONO) and nitrate (IONO2) iodides, are believed to impact tropospheric ozone levels. Guided by our quantum chemical calculations, we report the detection of INO in the gas phase by high-resolution spectroscopy for the first time. INO was generated by mixing continuously I2 and NO. The measurement and least-squares analysis of 173 a-type rotational transitions resulted in the accurate determination of molecular parameters.

International audience; A concerted hydrogen atom transfer mechanism has been elucidated for the isomerization of trans-HCOH to H(2)CO using a variety of ab initio and density functional theory methods. This work places specific emphasis on the role water molecules can play as a catalyst for this reaction and the mechanism by which this is achieved. This is of particular importance in the context of molecular ices in the interstellar medium because the presence of water in this reaction reduces the activation energy by at least 80%, which is accompanied by a significant enhancement of the reaction rate, at ≤300 K.

International audience; The electronic spectroscopy of isolated toluene in the gas phase has been investigated using high-resolution photoabsorption spectroscopy in the 4.0–10.8 eV energy range, with absolute cross-section measurements derived. We present the first set of ab initio calculations (vertical energies and oscillator strengths), which we use in the assignment of valence and Rydberg transitions of the toluene molecule. The spectrum reveals several new features not previously reported in the literature, with particular relevance to 7.989 and 8.958 eV, which are here tentatively assigned to the π*(17a′) ← σ(15a′) and 1π*(10a″) ← 1π(14a′) transitions, respectively. The measured absolute photoabsorption cross sections have been used to calculate the photolysis lifetime of toluene in the upper stratosphere (20–50 km).

International audience; We present the first set of ab initio calculations (vertical energies and oscillator strengths) of the valence and Rydberg transitions of the anaesthetic compound halothane (CF3CHBrCl). These results are complemented by high-resolution vacuum ultraviolet photoabsorption measurements over the wavelength range 115–310 nm (10.8–4.0 eV). The spectrum reveals several new features that were not previously reported in the literature. Spin–orbit effects have been considered in the calculations for the lowest-lying states, allowing us to explain the broad nature of the 6.1 and 7.5 eV absorption bands assigned to σ*(C–Br) ← nBr and σ*(C–Cl) ← nCl transitions. Novel absolute photoabsorption cross sections from electron scattering data were derived in the 4.0–40.0 eV range. The measured absolute photoabsorption cross sections have been used to calculate the photolysis lifetime of halothane in the upper stratosphere (20–50 km).

International audience

International audience; The chlorine/water interface is of crucial importance in the context of atmospheric chemistry. Modeling the structure and dynamics at this interface requires an accurate description of the interaction potential energy surfaces. We propose here an analytical intermolecular potential that reproduces the interaction between the Cl2 molecule and a water molecule. Our functional form is fitted to a set of high level ab initio data using the coupled-cluster single double (triple)/aug-cc-p-VTZ level of electronic structure theory for the Cl2 − H2O complex. The potential fitted to reproduce the three minima structures of 1:1 complex is validated by the comparison of ab initio results of Cl2 interacting with an increasing number of water molecules. Finally, the model potential is used to study the physisorption of Cl2 on a perfectly ordered hexagonal ice slab. The calculated adsorption energy, in the range 0.27 eV, shows a good agreement with previous experimental results.

International audience; We report on the measurements of the electron impact electronic excitation cross sections for XF4 (X = C, Si and Ge) molecules at 100 eV, 5° scattering angle and 30 eV, 30° in the electron energy loss range 8.0 - 18 eV. For a target of GeF4 molecule, the optically-forbidden behavior has been observed in the lower electron energy loss range.

International audience; Bromoiodomethane, CH2BrI, is a molecule of natural origin emitted in significant amount into the marine boundary layer. It can easily be decomposed by solar radiation, releasing Br and I atoms in the troposphere, which in turn impacts the atmospheric chemistry. Spectroscopy is an invaluable tool to monitor species present in the atmosphere. Since no high-resolution spectroscopic studies are available for this dihalomethane, we have investigated the rotational spectra of the two bromine isotopologues of CH2BrI in its vibrational ground state in the microwave and millimeter-wave regions. Transitions of b-type have been recorded by Fourier transform microwave spectroscopy below 25 GHz while both a- and b-type spectral lines have been measured below 230 GHz. Observed transitions correspond to energy levels with J ≤ 132 and Ka ≤ 14. Molecular constants including those describing the nuclear quadrupole coupling tensors for 79Br, 81Br, and 127I were accurately determined from the least-squares analysis of a total of 1873 distinct transition frequencies (of which 943 belong to the CH279BrI isotopologue). An experimental (r0) structure of the title species has been derived from the two sets of rotational constants.

International audience; In this contribution we probe BF3 low-lying excited singlet states measured at 100 eV, 2.8° scattering angle and triplet states at 40 eV, 40° scattering angle, while sweeping the energy loss over the range 10.0-20.0 eV. The electronic state spectroscopy has been investigated and the assignments supported by quantum chemical calculations. This provides the first comprehensive investigation of all singlet and triplet excited electronic states of boron trifluoride up to the first ionization potential. A generalized oscillator strength analysis is employed to derive oscillator strength f0 value and integral cross sections (ICSs) from the corresponding differential cross sections (DCSs). The f0 value is compared with the optical oscillator strength (OOS) from photoabsorption, and the unscaled Born ICSs are then compared with relevant energy and binary-encounter and f-scaled Born cross section (BEf-scaling) results determined as a part of this investigation. The lowest n members of the Rydberg series have been assigned as converging to the lowest ionization energy limits of boron trifluoride and classified according to the magnitude of the quantum defects (δ).

High level (CASSCF-MRCI) ab initio calculations are used to investigate the structural, electronic and vibrational properties of the electronic ground state of thiazyl chloride (NSCl) and of the low-lying electronic states of NSCl + . A new high resolution HeI photoelectron spectrum of NSCl has been recorded in the 10–16 eV energy region. From the results of the calculations, the first band is assigned to the (1) 2 A ′ state of NSCl + . The second one corresponds to the (2) 2 A ′ and (1) 2 A ″ states which are quasi-degenerate. Despite the high resolution, the two first bands show no vibrational fine structure. For the first one, Franck–Condon analysis shows that it is due to the overlapping of two vibrational progressions involving the S–Cl stretching and the NSCl bending modes. In the case of the second band, it is explained by the highly repulsive character of the potential energy surfaces of two states of NSCl + in the Franck–Condon region of the neutral molecule. For the third band, which shows vibrational peaks, the calculation of Franck–Condon factors permits the determination of the adiabatic ionisation energy of the (3) 2 A ′ electronic state of NSCl + at 13.798 eV. Finally, the fourth band, which is due to three different ionic states with vibrational progressions, is too complicated to be assigned quantitatively.

International audience; The carbon and oxygen K-shell spectra of gaseous 2-propenal (acrolein) have been measured using the inner-shell electron energy loss spectroscopy method. Large scale ab initio configuration interaction calculations have been carried out to enable firm assignments of the observed bands. The overall shapes of the spectra are similar to previous low resolution monolayer and multilayer phases NEXAFS spectra recorded by photoabsorption of synchrotron radiation, but the spectral bands are much better resolved than the earlier ones. The spectra are dominated by excitation of π* type states and by interaction between the C=C and C=O π* orbitals.

9 pags.; 5 figs.; 3 tabs., We report on measurements of differential cross sections (DCSs) for electron impact excitation of a series of Rydberg electronic-states in α-tetrahydrofurfuryl alcohol (THFA). The energy range of these experiments was 20-50 eV, while the scattered electron was detected in the 10°-90° angular range. There are currently no other experimental data or theoretical computations against which we can directly compare the present measured results. Nonetheless, we are able to compare our THFA DCSs with earlier cross section measurements for Rydberg-state electronic excitation for tetrahydrofuran, a similar cyclic ether, from Do et al. [J. Chem. Phys. 134, 144302 (2011)]. In addition, >rotationally averaged>elastic DCSs, calculated using our independent atom model with screened additivity rule correction approach are also reported. Those latter results give integral cross sections consistent with the optical theorem, and supercede those from the only previous study of Milosavljevićet al. [Eur. Phys. J. D 40, 107 (2006)]. © 2014 AIP Publishing LLC., Spanish Ministerio de Economia y Competitividad under Project No. FIS2012-31230) funding agencies who financially supported various aspects of this work

International audience; : The electronic spectroscopy of isolated tetrahydrofurfuryl alcohol (THFA) in the gas phase has been investigated using high-resolution photoabsorption spectroscopy in the 5.0-10.8 eV energy-range, with absolute cross-section measurements derived. The He(I) photoelectron spectrum was also collected to quantify ionization energies in the 9-16 eV spectral region. These experiments are supported by the first high-level ab initio calculations performed on the excited states of the neutral molecule and on the ground and excited state of the positive ion. The good agreement between the theoretical results and the measurements allows us to quantify for the first time the electronic-state spectroscopy of THFA. The present work also considers the question of the lowest energy conformers of the molecule and its population distribution at room temperature.

The highest resolution vacuum ultraviolet photoabsorption spectrum of ethyl formate, C2H5OCHO, yet reported is presented over the wavelength range 115.0–275.5 nm (10.75–4.5 eV) revealing several new spectral features. Valence and Rydberg transitions and their associated vibronic series, observed in the photoabsorption spectrum, have been assigned in accordance with new ab initio calculations of the vertical excitation energies and oscillator strengths. Calculations have also been carried out to determine the ionization energies and fine structure of the lowest ionic state of ethyl formate and are compared with a newly recorded He(I) photoelectron spectrum (from 10.1 to 16.1 eV). New vibrational structure is observed in the first photoelectron band. The photoabsorption cross sections have been used to calculate the photolysis lifetime of ethyl formate in the upper stratosphere (20–50 km).

We report the first global potential energy surface (PES) for the X(2)A' ground electronic state of the Si((3)P) + OH(X(2)Π) → SiO(X(1)Σg(+)) + H((2)S) reaction. The PES is based on a large number of ab initio energies obtained from multireference configuration interaction calculations plus Davidson correction (MRCI+Q) using basis sets of quadruple zeta quality. Corrections were applied to the ab initio energies in the reactant channel allowing a proper description of long-range interactions between Si((3)P) and OH(X(2)Π). An analytical representation of the global PES has been developed by means of the reproducing kernel Hilbert space method. The reaction is found barrierless. Two minima, corresponding to the SiOH and HSiO isomers, and six saddle points, among which the isomerization transition state, have been characterized on the PES. The vibrational spectra of the SiOH/HSiO radicals have been computed from second-order perturbation theory and quantum dynamics methods. The structural, energetic, and spectroscopic properties of the two isomers are in good agreement with experimental data and previous high quality calculations.