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Energy-Efficient Ammonia Production from Air and Water Using Electrocatalysts with Limited Faradaic Efficiency

Coastal environments are nitrogen (N) removal hot spots, which regulate the amount of land-derived N reaching the open sea. However, mixing between freshwater and seawater creates gradients of inorganic N and bioavailable organic matter, which affect N cycling. In this study, we compare nitrate reduction processes between estuary and offshore archipelago environments in the coastal Baltic Sea. Denitrification rates were similar in both environments, despite lower nitrate and carbon concentrations in the offshore archipelago. However, DNRA (dissimilatory nitrate reduction to ammonium) rates were higher at the offshore archipelago stations, with a higher proportion of autochthonous carbon. The production rate and concentrations of the greenhouse gas nitrous oxide (N2O) were higher in the estuary, where nitrate concentrations and allochthonous carbon inputs are higher. These results indicate that the ratio between nitrate and autochthonous organic carbon governs the balance between N-removing denitrification and N-recycling DNRA, as well as the end-product of denitrification. As a result, a significant amount of the N removed in the estuary is released as N2O, while the offshore archipelago areas are characterized by efficient internal recycling of N. Our results challenge the current understanding of the role of these regions as filters of land-to-sea transfer of N.

The dissociation process of hydrogen molecules on W(110) was studied using density functional theory and classical molecular dynamics. We have calculated the dissociation probability for molecules with energies below 300 meV and analyzed the dynamics of the adsorption process. Our results show that the fate of each trajectory is determined at distances relatively far from the surface, at roughly 2–2.5 Å. This distance varies slightly with the initial kinetic energy of the molecule. Part of our simulations include van der Waals dispersion effects in the interaction between molecule and surface. We present a comparison between these results and other theoretical and experimental results previously published. The inclusion of the van der Waals term provokes an increase in the far-distance attraction that is compensated by a stronger repulsion at short distances. The combination of both effects appreciably decreases the value of the dissociation probability. The successful comparison of our results with experimental information confirms that the methodology employed can be considered as a rich and accurate instrument to study the dissociation of hydrogen on surfaces., A. R. F. acknowledges financial support by the University of Bordeaux. This work was conducted in the scope of the transborder joint Laboratory “QuantumChemPhys: Theoretical Chemistry and Physics at the Quantum Scale” (ANR-10-IDEX-03-02). This work has been supported in part by the Basque Departamento de Educación, Universidades e Investigación, the University of the Basque Country UPV/EHU (Grant No. IT1246-19) and the Spanish Ministerio de Ciencia e Innovación (PID2019-107396GB-I00/AEI/10.13039/501100011033).

Nuclear and electronic dynamics in a wavepacket comprising bound Rydberg and valence electronic states of nitrogen from 12 to 15 eV are investigated using attosecond transient absorption. Vibrational quantum beats with a fundamental period of 50 femtoseconds persist for a picosecond in the b′ 1Σ+u valence state. Multi-state calculations show that these coherences result primarily from near infrared-induced coupling between the inner and outer regions of the b′ 1Σ+u state potential and the dark a″ 1Σ+g state. The excellent spectral and temporal resolution of this technique allows measurement of the anharmonicity of the b′ 1Σ+u potential directly from the observed quantum beats.

Continuous nitrogen gas (N-2) flushing extends the shelf life of raw milk (RM) during cold storage. The effect of N-2 treatment on the total antioxidant capacity (TAC) and ascorbic acid (AA) content of RM was determined during cold storage. TAC of RM or deproteinized RM was determined by ABTS and DPPH methods, while L(+)-AA content of RM was determined chromatographically on days 0, 4 and 7 during storage at 6 +/- 1 degrees C. With the ABTS method, the TAC of RM decreased from 472.33 +/- 16.70 to 369.47 +/- 62.06 mu M TEAC while it reduced from 13.30 +/- 0.84 to 8.20 +/- 0.66 mu M TEAC with DPPH method during cold storage. TAC of RM determined with ABTS method decreased after 4 day-storage; however, they remained statistically similar for N-2-treated samples during 7 day-storage. The AA content of RM ranged from 14.06 to 10.76 mg/L during storage but N-2-treatment did not influence AA content significantly. Deproteinization reduced TAC values of milk samples significantly, and the reduction with the ABTS method was about 47.50 % for control samples cold-stored for four days, while it was 11.67 % for N-2-treated deproteinized RM. In conclusion, N-2-flushing through the headspace of milk containing vessels showed a significant protective effect on the antioxidant components of RM during cold storage.

The electrochemical synthesis of ammonia from nitrogen under mild conditions using renewable electricity is an attractive alternative1–4 to the energy-intensive Haber–Bosch process, which dominates industrial ammonia production. However, there are considerable scientific and technical challenges5,6 facing the electrochemical alternative, and most experimental studies reported so far have achieved only low selectivities and conversions. The amount of ammonia produced is usually so small that it cannot be firmly attributed to electrochemical nitrogen fixation7–9 rather than contamination from ammonia that is either present in air, human breath or ion-conducting membranes9, or generated from labile nitrogen-containing compounds (for example, nitrates, amines, nitrites and nitrogen oxides) that are typically present in the nitrogen gas stream10, in the atmosphere or even in the catalyst itself. Although these sources of experimental artefacts are beginning to be recognized and managed11,12, concerted efforts to develop effective electrochemical nitrogen reduction processes would benefit from benchmarking protocols for the reaction and from a standardized set of control experiments designed to identify and then eliminate or quantify the sources of contamination. Here we propose a rigorous procedure using 15N2 that enables us to reliably detect and quantify the electrochemical reduction of nitrogen to ammonia. We demonstrate experimentally the importance of various sources of contamination, and show how to remove labile nitrogen-containing compounds from the nitrogen gas as well as how to perform quantitative isotope measurements with cycling of 15N2 gas to reduce both contamination and the cost of isotope measurements. Following this protocol, we find that no ammonia is produced when using the most promising pure-metal catalysts for this reaction in aqueous media, and we successfully confirm and quantify ammonia synthesis using lithium electrodeposition in tetrahydrofuran13. The use of this rigorous protocol should help to prevent false positives from appearing in the literature, thus enabling the field to focus on viable pathways towards the practical electrochemical reduction of nitrogen to ammonia. A protocol for the electrochemical reduction of nitrogen to ammonia enables isotope-sensitive quantification of the ammonia produced and the identification and removal of contaminants.

Because of the limited number and size of the oil extraction opportunities, olives are generally piled and stored at ambient temperatures for weeks before processing. Under these conditions biochemical changes could result a negative affect on the olive quality. The changes in the olive result poor stability in olive oil because of the oxidation and decomposition of bioactive compounds such as phenolic substances. Indeed, it is known that polyphenols are a large family of compounds found in plant tissues, which show strong antioxidant activity. The healthy characteristic of the phenolic compounds is associated to their radical scavenging activities. In this study, Gemlik olives cultivated from Osmaniye area were stored for 25 days at 5 °C under three different conditions (20 kPa CO 2 atmosphere, 20 kPa N 2 atmosphere and air). Olive oil was extracted following of 0, 5, 15 and 25 days of olive fruits storage. Qualtiy markers (free fatty acidity, peroxide value, K 270 and K 232 ) together with the phenolic compounds and fatty acid compositions of oils were determined. The physical properties of olives (flesh/pit ratio, average weight and fruit firmness) were well-preserved under CO 2 and N 2 atmospheres. The phenolics (tyrosol, syringic acid, vanilin, p-coumaric acid, oleuropein, cinnamic acid and luteolin) and fatty acids (palmitic, palmiteloic, heptadecanoic, heptadecenoic, stearic, oleic, linoleic, linolenic, arachidic, behenic, docosadienoic and lignoceric acids) composition were generally unchanged during storage. Oleuropein, the bitter principle of olives disapperead faster in the oils obtained through storage under N 2 than other storage conditions. © 2018, Springer Science+Business Media, LLC, part of Springer Nature. OKÜBAP-2015-PT3-011 ?Each data point represents mean of three replicates ± SD aSmall letters indicate significance for olive storage duration within each treatment (p < 0.05) ACapital letters indicate significance at a given storage time between treatments (p < 0.05) Acknowledgements Many thanks to Osmaniye Korkut Ata University Research Council for funding this research (OKÜBAP-2015-PT3-011). Many thanks also go to Prof. Ziya Günata for proofreading the manuscript.

The compression of ammonium azide (AA) has been considered to be a promising route for producing high energy-density polynitrogen compounds. So far though, there is no experimental evidence that pure AA can be transformed into polynitrogen materials under high pressure at room temperature. We report here on high pressure (P) and temperature (T) experiments on AA embedded in N2 and on pure AA in the range 0–30 GPa, 300–700 K. The decomposition of AA into N2 and NH3 was observed in liquid N2 around 15 GPa–700 K. For pressures above 20 GPa, our results show that AA in N2 transforms into a new crystalline compound and solid ammonia when heated above 620 K. This compound is stable at room temperature and on decompression down to at least 7.0 GPa. Pure AA also transforms into a new compound at similar P–T conditions, but the product is different. The newly observed phases are studied by Raman spectroscopy and X-ray diffraction and compared to nitrogen and hydronitrogen compounds that have been predicted in the literature. While there is no exact match with any of them, similar vibrational features are found between the product that was obtained in AA + N2 with a polymeric compound of N9H formula.

Nanoporous materials used in industrial applications (e.g., catalysis and separations) draw their functionality from properties at the nanoscale (1 – 10 Å). When shaped into a technical form these solids reveal spatial variations in the same properties over much larger length scales (1 µm – 1 cm). The multiscale characterization of these systems is impaired by the trade‐off between sample size and image resolution that is bound to the use of most imaging techniques. We show here the application of X‐ray computed tomography for the non‐invasive spatial characterization of a zeolite/activated carbon adsorbent bed across three orders of magnitude in scale. Through the unique combination of gas adsorption isotherms measured locally and their interpretation by physisorption analysis, we determine three‐dimensional maps of the specific surface area and micropore volume. We further use machine learning to identify and locate the materials within the packed bed. This novel ability to reveal the extent of heterogeneity in technical porous solids will enable a deeper understanding of their function in industrial reactors. Such developments are essential towards bridging the gap between material research and process design.

The preparation and reactivity of a novel molybdenum dinitrogen complex supported by a nitrogen-centred tripodal phosphine ligand (N-triphos, N(CH2PPh2)3, NP3Ph) are reported. Reaction of N-triphos with [MoX3(THF)3] (X = Cl, Br, I) gave the Mo(III) complex [MoX3(κ2-NP3Ph)(THF)] (1), where bidentate N-triphos coordination was observed. Reduction of this complex in the presence of dppm (bis(diphenylphosphino)methane) gave the dinitrogen complex [Mo(N2)(dppm)(κ3-NP3Ph)] (2), which exhibits moderate dinitrogen activation. An additional hydride complex, [Mo(H)2(dppm)(κ3-NP3Ph)] (4), was produced either as a minor side product during the reduction step, or as a major product by direct hydrogenation of the dinitrogen complex 2. The reactivity of the dinitrogen complex 2 with a range of Lewis acids was also investigated. At low temperatures, protic or borane Lewis acids (H+, BBr3 and tris(pentafluorophenyl)borane (BCF)) were found to coordinate to the apical nitrogen atom of the N-triphos ligand, with no conclusive evidence of any functionalisation of the dinitrogen ligand. Alkali metal Lewis acid addition to 2 resulted in the unexpected rearrangement of the N-triphos ligand to form [Mo(dppm)(PMePh2)(PCP)][B(C6F5)4] (7), where PCP, [Ph2PCNHCH2PPh2] is the carbenic ligand formed upon rearrangement from the reaction of 2 with M[B(C6F5)4] (M = Li, Na or K). Single crystal X-ray diffraction of complexes 1, 2, 4 and 7 provided structural confirmation of the N-triphos molybdenum complexes described.

Physical review / A 95(4), 043419(2017). doi:10.1103/PhysRevA.95.043419, By theoretical calculation, we demonstrate the possibility to control and partially suppress the Coulomb explosion of N$_2$ molecules after core-level photoionization by an x-ray laser and subsequent Auger decay. This is achieved by means of a femtosecond infrared laser pulse interacting with the N$_{2}$$^{2+}$ dication produced by the x-ray pulse. Suppression of molecular fragmentation requires few-femtosecond IR pulses interacting with the system either during or shortly after the arrival of the x-ray pulse. The IR pulse suppresses fragmentation mostly by optically coupling the electronic routes to ultrafast molecular dissociation with electronic channels able to support long-lived vibrational resonances. The effect is strongly dependent on the orientation of the molecule with respect to the polarization axis of the IR field. Our calculations are motivated by x-ray pump–IR probe experiments performed at an x-ray free-electron laser [J. M. Glownia et al., Opt. Express 18, 17620 (2010)], where only enhancement of N$_{2}$$^{2+}$ fragmentation as a function of the pump-probe delay time was reported. The opposite effect reported here becomes apparent when the various electronic channels are considered separately. In practice, this corresponds to a coincident measurement of the energy of the ejected Auger electron., Published by APS, Woodbury, NY

Sulfur dioxide (SO2) is a molecule of considerable interest for both atmospheric chemistry and astrophysics. In the Earth’s atmosphere, it enters in the sulfur cycle and it is ubiquitous present in polluted atmospheres, where it is responsible for acid rains. It is also of astrophysical and planetological importance, being present on Venus and in interstellar clouds. In this work the collisional broadening of a number of ν1 ro-vibrational lines of SO2 perturbed by N2, O2 and He are investigated at room temperature in the 9 μm atmospheric region by means of high resolution tunable diode laser (TDL) infrared spectroscopy. From N2- and O2-broadening coefficients, the broadening parameters of sulfur dioxide in air, useful for atmospheric applications, are derived as well. From the present measurements some conclusions on the quantum number dependence of the N2-, O2- and He-broadening coefficients are drawn. While the J dependence is weak for all the perturbers investigated, different trends with Ka are reported. N2-broadening coefficients show a slight decrease with increasing values of Ka, whereas O2 and He broadening cross sections first increase up to K a ″ ≈ 6 and then they keep a nearly constant value. A comparison and a brief discussion on the efficiency of self-, N2-, O2- and He-collisional dynamics are given. The data obtained represent a significant analysis on foreign broadening of SO2 useful for atmospheric remote sensing and astrophysical applications.

N-doped and N, S-codoped titania powders were prepared applying simple chemical treatment with various modifiers. The N and S were introduced preserving the crystalline structure, morphology and specific surface area of the initial TiO2. The level of N, S doping varied depending on the modifier two of which were structural isomers. In all samples, N was found interstitially incorporated in the TiO2 lattice. S was recorded in ionic states S6+ and S4+. All modified powders exhibited enhanced visible light absorption and narrower energy band gap in comparison to the initial titania. Except for the N-doped titania, the photocatalytic activity in NOx oxidation under UV light decreased after doping, while the activity under visible light did not increase for all modified samples. This outcome was related to the high level of N and S doping and intense e(-)-h(+) recombination on dopants' sites. The activity of the photocatalysts in NOx oxidation processes was also connected to the type of non-metal dopant in the lattice of TiO2. The beneficial effect of N-doping was ascribed to the preferential formation of center dot OH species on N-doped surface, whereas the detrimental effect of N, S-codoping was credited to the suppressed center dot OH production on S-doped surface. (C) 2012 Elsevier B.V. All rights reserved. Catalysis Today

Outlier diagnostic in phase equilibrium data of binary clathrate hydrates containing CO 2 is the main aim of the present work. The treated experimental data are concerning the clathrate hydrates of CO 2 + CH 4 /N 2 in the presence of water. The utilized algorithm applies the basis of a mathematical approach, in which the statistical Hat matrix, Williams plot, and the residuals of two models results bring about the probable outliers detection. The range of applicability of the applied models and quality of the existing experimental data are also investigated. The van der Waals and Platteeuw (vdW–P) solid solution theory is used to model the hydrate phase, and the Valderrama–Patel–Teja equation of state (VPT-EoS) along with the non-density dependent (NDD) mixing rules is applied to deal with the fluid phases in the first model. The compositions of the vapor phase in equilibrium with gas hydrate and liquid water as well as the equilibrium pressures are predicted through the mentioned model. The second model includes a correlation proposed by Adisasmito et al., which is utilized to represent the hydrate dissociation pressures for three-phase equilibrium conditions (liquid water–vapor–hydrate). It is interpreted from the obtained results that the applied models for calculation/estimation of the phase behavior of the investigated binary clathrate hydrate systems have wide ranges of applicability. Consequently, we may, with high confidence level, say that among all data treated, one experimental equilibrium pressure value and four experimental hydrate dissociation values are probable doubtful ones.

Soils can be a source and sink for atmospheric nitrous oxide (N2O). Consumption of N2O has been reported for anoxic soils and sediments rich in organic matter and depleted in nitrates ( NO 3 − ), and also for some dry, oxic soils. However, the mechanisms and controls of N2O consumption in dry soil are not clear. Here, we report on a field study in China (Taihang mountain region, Shijiazhuang), in which N2O uptake by a sandy loam soil was measured for the greater part of the season (from April to October in 2011), and on four incubation experiments, in which we tried to reveal the roles of water content and oxygen (O2) concentrations on N2O consumption. Flux measurements in the field were made bi-weekly on unfertilized cropped land with static flux chambers (5 replicates) for 6 months. The results show that N2O–N fluxes ranged from −26.0 to −726.6 μg m−2 h−1. Consumption of N2O was largest when the soil was dry (5–20% soil water filled pore space). In the incubation experiments, N2O consumption and N2 production were measured in (an)aerobic soil with soil moisture content ranging from 1% to 50% (wt/wt) and with N2O addition, using a thermostatic, robotized incubation system. Under anaerobic conditions, N2O was rapidly consumed at water content of >10% (wt/wt). However, a significant consumption also occurred at 1% soil moisture. Under aerobic conditions, N2O consumption increased with increasing soil moisture content, but significant consumption was still measured at 2% moisture. Sterilization of oxic soil completely blocked N2O consumption, suggesting that the consumption had a biological nature. In conclusion, the steady N2O consumption measured in the field was confirmed by the laboratory experiments, but the relationship with soil moisture content was reversed. Further studies are required to understand this apparent anomaly.

Atomically detailed simulations were used to examine CO2/N-2 separation potential of metal organic framework- (MOF-) based mixed matrix membranes (mmms) in this study. Gas permeability and selectivity of 700 new mmms composed of 70 different mofs and 10 different polymers were calculated for CO2/N-2 separation. This is the largest number of MOF-based mmms for which computational screening is done to date. Selecting the appropriate mofs as filler particles in polymers resulted in mmms that have higher CO2/N-2 selectivities and higher CO2 permeabilities compared to pure polymer membranes. We showed that, for polymers that have low CO2 permeabilities but high CO2 selectivities, the identity of the MOF used as filler is not important. All mofs enhanced the CO2 permeabilities of this type of polymers without changing their selectivities. Several MOF-based mmms were identified to exceed the upper bound established for polymers. The methods we introduced in this study will create many opportunities to select the MOF/polymer combinations with useful properties for CO2 separation applications., Scientific and Technological Research Council of Turkey (TÜBİTAK)

Adsorption, 18 (1), ISSN:0929-5607, ISSN:1572-8757

Hydrofluorocarbons have been used as replacement gases of chlorofluorocarbons, since the latter have been phased out by the Montreal Protocol due to their environmental hazardous ozone-depleting effects. This is also the case of difluoromethane (CH2F2, HFC-32), which nowadays is widely used in refrigerant mixtures together with CF3CH3, CF3CH2F, and CF3CHF2. Due to its commercial use, in the last years, the atmospheric concentration of HFC-32 has increased significantly. However, this molecule presents strong absorptions within the 8–12 μm atmospheric window, and hence it is a greenhouse gas which contributes to global warming. Although over the years several experimental and theoretical investigations dealt with the spectroscopic properties of CH2F2, up to now pressure broadening coefficients have never been determined. In the present work, the line-by-line parameters of CH2F2 are retrieved for either ground state or ν7 band transitions by means of microwave (MW) and infrared (IR) absorption spectroscopy, respectively. In particular, laboratory experiments are carried out on 9 pure rotational transitions of the ground state and 26 ro-vibrational transitions belonging to the ν7 band lying around 8.2 μm within the atmospheric region. Measurements are carried out at room temperature on self-perturbed CH2F2 as well as on CH2F2 perturbed by N2 and O2. The line shape analysis leads to the first determination of self-, N2-, O2-, and air-broadening coefficients, and also of line intensities (IR). Upon comparison, broadening coefficients of ground state transitions are larger than those of the ν7 band, and no clear dependence on the rotational quantum numbers can be reported. The obtained results represent basic information for the atmospheric modelling of this compound as well as for remote sensing applications.

Molecular dynamics simulations have been used to study the effects of the corrugation in the holding potential of nitrogen molecules on the structure of fluid monolayer and submonolayer films of the molecules on a solid substrate. Structures of monolayer and submonolayer fluid films of nitrogen molecules adsorbed on graphite and on a model uncorrugated “smooth” graphite surface are compared. For films on the “smooth” graphite surface the melting temperature is lowered by 7 K. Contrary to what is found for films on the corrugated surface, the simulations show that there is a region of liquid–gas coexistence, demonstrating that this is a normal triple point system. A discrepancy between calculated and experimental melting temperatures of submonolayer films was traced to the intermolecular potentials. These have been tested by comparing molecular dynamics simulations of isosteric heats of adsorption in fluid films with experimental measurements. The establishment of the effects of the corrugation in the hold...

The melting mechanism in submonolayer films of ${\mathrm{N}}_{2}$ molecules adsorbed on the basal planes of graphite is studied using molecular-dynamics simulations. The melting is strongly correlated with the formation of vacancies in the films. As the temperature increases, the edges of the submonolayer patch become atomically rough and vacancies are first created there. Then there is an onset temperature at which the vacancies penetrate into the patch. At an intermediate region of coverages \ensuremath{\sim}0.3\char21{}0.8 commensurate layers, there is sufficient free volume for the film to melt at that temperature. At higher coverages, \ensuremath{\sim}0.8\char21{}1.0 layers, a solid with defects is formed, and additional free volume must be created by higher energy mechanisms such as layer promotion for melting to occur; thus, the melting temperature rises with coverage. In contrast, for very small patches, the atomically rough zone penetrates the entire patch at a lower temperature where the film melts. The calculated melting temperatures are significantly lower than observed experimentally, indicating a severe fault in the potential model. A possible source of the discrepancy is identified.

(E)-2,4-Dinitro-N-((2E,4E)-4-phenyl-5-(pyrrolidin-1-yl)penta-2,4-dienylidene) aniline dye was prepared in one pot by reaction of premade N-2,4-dinitrophenyl-3-phenylpyridinium chloride (DNPPC) and pyrrolidine in absolute MeOH.

International audience; Combined spatially resolved electron-energy loss spectroscopy (EELS) and high resolution near-edge X-ray absorption fine structure (NEXAFS) spectroscopy have been used to investigate the nitrogen doping of multi-walled carbon nanotubes (N-MWNT). EELS indicates that most of the tubes are nitrogen-doped. NEXAFS spectroscopy reveals pyridine-like and nitrile N structures. High resolution NEXAFS experiments show that the main nitrogen concentration originates from a high amount of molecular N-2 encapsulated into only a small quantity of tubes.

International audience; Rotational coherent anti-Stokes Raman spectroscopy (CARS) is a well-established spectroscopic technique for thermometry at pre-combustion temperatures an atmospheric pressure. However, at pressures of several MPa, a previous investigation revealed large discrepancies between experimental data and the theoretical model. A re-evaluation has been made of these data (at room temperature and in the range 1.5-9 MPa) with two improvements to the spectral code. The first is the inclusion of an inter-branch interference effect, which is described in detail in Paper I. The second is the use of experimental S-1-branch Raman line widths measured at 295 K, with a temperature dependence extracted from semi-classical calculations following the Robert-Bonamy formalism. It is shown that these two modifications significantly improve the theoretical model, since both the spectral fits and the accuracy of the evaluated temperatures are considerably improved.

International audience; The paper presents high resolution Raman investigations of the Q(1) line of H-2 in Ar mixture from low density (Doppler regime) to high density (collisional regime) analyzed with a unique line shape profile. Measurements are performed by stimulated Raman gain spectroscopy between 300 and 1000 K in a wide density range (from 0.2 to 11 amagat). All the observed spectral features are accurately described by a unified model recently proposed by two of the authors. This model accounts for a velocity-memory process, not restricted to the usual hard and soft limits. It also includes correlation between velocity- and phase-changing collisions. An exhaustive analysis of various possible mechanisms on the line shape is achieved. These mechanisms are the Dicke narrowing, the radiator speed dependence of the collisional broadening and shifting parameters, the collisionally induced speed-class exchange and the nonimpact effect. The present test shows the high consistency of the unified model, since it allows one to get a remarkable agreement with all the data by using a unique set of parameters. This model should be useful for optical diagnostics at moderate density, as required for combusting media or atmospheric work.

0377-0486; Line shifting and broadening coefficients of the anisotropic S(J) lines (v = 0, J --> v = 1, J + 2) of the nitrogen molecule were measured at room temperature using high-resolution stimulated Raman spectroscopy. A rotational quantum number dependence of the S(J) line shifts was observed. In order to avoid an asymmetry of experimental origin, a suitable theoretical profile was fitted to the experimental lineshapes. This study allows the testing of the theoretical methods for calculating the line broadening coefficients in anisotropic Raman scattering, which have already been used in the analysis of infrared absorption data. The behaviour of the modified sum rule and the RPA (random phase approximation) methods was studied.

The zeroth (Σ0), second order (Σ2), quasiparticle second order (Σ2q), diagonal two‐particle one‐hole Tamm Dancoff approximation (Σ2ph‐TDA) and the quasiparticle diagonal 2ph‐TDA (Σq2ph‐TDA) decouplings have been applied to investigate the 2Π CO− and 2B2g C2H4− shape resonances. An examination of the resonant roots and the corresponding Feynman Dyson amplitudes (FDAs) reveals that the most economic and effective description is offered by the second order decoupling. The more demanding diagonal two‐particle one‐hole Tamm Dancoff approximation (2ph‐TDA) is shown to be less effective and the quasiparticle decouplings are shown to be no better than the zeroth order (bivariational self‐consistent field) approximation in the description of molecular shape resonances. The correlation and relaxation effects incorporated by the Σ2 and Σ2ph‐TDA decouplings are shown to assist resonance formation by lowering the antibonding nature of the lowest unoccupied molecular orbitals (LUMOs) on the real line and by turning the...

Vibrational excitation (nu(f)--nu(i)) cross-sections sigma(nu(f)--nu(i) )(E) in resonant e-N(2) and e-H(2) scattering are calculated from transition matrix elements T(nu(f),nu(i) )(E) obtained using Fourier transform of the cross correlation functionphi(nu(f) )(R)|psi(nu(i))(R,t), where psi(nu(i))(R,t) approximately =e(-iH(A(2))-(R)t/h phi(nu(i))(R) with time evolution under the influence of the resonance anionic Hamiltonian H(A(2) (-))(A(2) (-)=N(2)(-)/H(2) (-)) implemented using Lanczos and fast Fourier transforms. The target (A(2)) vibrational eigenfunctions phi(nu(i))(R) and phi(nu(f))(R) are calculated using Fourier grid Hamiltonian method applied to potential energy (PE) curves of the neutral target. Application of this simple systematization to calculate vibrational structure in e-N(2) and e-H(2) scattering cross-sections provides mechanistic insights into features underlying presence/absence of structure in e-N(2) and e-H(2) scattering cross-sections. The results obtained with approximate PE curves are in reasonable agreement with experimental/calculated cross-section profiles, and cross correlation functions provide a simple demarcation between the boomerang and impulse models.