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The structural parameters of the three most stable isomers with formula Cl2O2, dichlorine peroxide, chloryl chloride and chlorine chlorite, were determined by high-level ab initio theory. The effects of core-valence electronic correlation as well as relativistic corrections were included in the calculations, and vibrational averaging of the so-obtained structures was performed. The bond distances agree with experimental data, where available, to within 0.01 Å, an unprecedented accuracy in particular for the floppy dichlorine peroxide molecule. The UV spectra of the three molecules were computed and decay pathways investigated. Under actinic UV radiation at 248 nm dichlorine peroxide decomposes principally according to ClOOCl → 2Cl + O2, in a synchronous concerted mechanism. In the low-energy tail region of this signal, the decay proceeds in a non-synchronous manner. There is also a low probability of the decay channel towards ClOO + Cl, whereas ClO molecules were not found. Chloryl chloride absorbs strongly around 300 nm. It disintegrates into ClO2 + Cl, where ClO2 seems to be formed mainly in excited electronic states which decompose further into Cl + O2. Hence chloryl chloride, though much less abundant in the stratosphere than dichlorine peroxide, also contributes to ozone depletion.

Context. The N2+ fluorescence spectrum of comet C/2016 R2 is modelled in a companion paper. That work relies on accurate Einstein coefficients for electric dipole transitions between the B2∑u+ and X2∑g+ electronic states of N2+. Aims. These coefficients are provided in the present paper. Methods. The potential energy curves and transition dipole moments were computed at a high level of ab initio theory and include relativistic corrections. Rovibrational wavefunctions were then obtained without assuming separability of vibrational and rotational motions. Results. Vibrationally and rotationally resolved Einstein coefficients are presented in a convenient three-parameter functional form for three isotopologues. A possible explanation is given for the large variation in the experimental radiative lifetimes.

We present a physical model that explains the dependence of the UV cross section of ClOOCl on temperature in the actinic wavelength region measured before by J.J. Lin, A.F. Chen and Y.T. Lee [Chemistry — An Asian Journal, 6, 1664–1678 (2011)]. It was unclear why there are frequency regions in which the cross section decreases with increasing temperature and others in which it increases. This interesting behaviour is now shown to be due to the non-rigidity of the molecule and can be described in terms of the Boltzmann populations of the lowest torsional states and small, non-systematic variations in their absorption cross sections. Combination of these two ingredients produces the non-trivial temperature effect.

International audience; We report on the structures of two conformers of 2-thiophenecarboxaldehyde as obtained using a combination of molecular jet Fourier-transform microwave spectroscopy and quantum chemical calculations. The microwave spectrum was recorded using two spectrometers operating in the frequency ranges of 2.0 to 26.5 GHz and 26.5 to 40.0 GHz. The spectra of all singly-substituted heavy atom isotopologues 13C, 18O and 34S in their natural abundances could be measured and assigned to determine the gas-phase substitution rs and semi-experimental reSE structures of the most abundant conformer. The spectrum of the 33S isotopologue with its nuclear quadrupole coupling hyperfine structure was analysed, yielding the complete quadrupole tensor with high accuracy. The experimental results are used to map the observed rotational constants to the corresponding molecular structure obtained from quantum chemical calculations, which predicted two conformers with an energy difference of about 6 kJ mol−1 at the MP2/6-311++G(d,p) level of theory. Insight into the conformational stability of aromatic heterocyclic carboxaldehydes and bond situations of the sulfur atom extracted from the hyperfine structure of the 33S nucleus are discussed within the frame of the current literature. This work provides an important contribution to the study and characterisation of sulfur-containing volatile organic compounds.

A new compound, 4-chlorobenzylammonium nitrate, was obtained by a reaction between 4-chlorobenzylamine and nitric acid, and characterized by X-ray diffraction and FT-IR spectroscopy. The phenyl ring and the nitro group were essentially coplanar in the obtained crystal. The aminomethyl substituent CH2 NH3+ lies out the plane of the aromatic ring as evidenced by the torsion angle Nl C7 C1 C6 of 88.2°. The crystal packing was formed by an infinite bi-dimensional layers with graph-set motif R48(16), and stabilized by N H⋯O hydrogen bond-type intermolecular interactions. In addition, molecular geometry in the electronic ground state, Hirshfeld surface, vibrational wavenumbers, molecular electronic plane (MEP), and Natural bond orbital (NBO) analysis were performed using the density functional theory (DFT/B3LYP) with 6-31+G* basis set. Theoretical and experimental results are in good agreement. The NBO analysis confirms that the N H⋯O intermolecular interactions notably affect crystal packing in this molecule.

The electrogeneration of pure 4,4′-di-tert-butylbiphenyl peroxide as an electrodeposit could be achieved on a platinum electrode through the anodic oxidation of p-tert butylphenol in the presence of Lutidine, in addition to several soluble oligomers. The electrochemical and theoretical studies have shown that the favored coupling reaction corresponds to the O–O bond, albeit it is generally being considered unstable. Without the strong base, a mixture of trimer, tetramer and pentamer was deposited. The peroxide product presents a different electroactivity to that of the phenolic compound, with the appearance of a redox process involving cathodic and anodic symmetrical peaks at −0.10/0.15 V versus SCE, which indicates the preference of the polymer to adhere onto the electrode surface. The thermal degradation has also been analyzed. Quantum-chemical calculations reveal the reason for the oxygen–oxygen coupling. The authors would like to thank the Tunisian Ministry of Higher Education and Research for its financial support as well as the King Saud University for its funding through the Research Group Project No RGP-VPP-243. They would also like to thank the Spanish Ministry of Economy and Competitiveness for its financial support and the STIs for the ERDF funds (MAT2013-42007-P) and the Generalitat Valenciana (PROMETEO2013/ 038).

To accurately characterize the large amplitude motions and soft degrees of freedom of isolated molecules, sampling their conformational landscape by molecular mechanics and quantum chemical calculations may provide a valuable insight into the structure and dynamics. However, the resulting models need to be validated by a reliable experimental counterpart. For ethyl pentanoates, which belong to the family of fruit esters, benchmark calculations at different levels of theory showed that the C-C bond in proximity to the ester carbonyl group exhibits a large amplitude motion that is extremely sensitive to the choice of quantum chemical method and basis set. In such cases, insights from high-resolution molecular jet techniques are ideal to accurately identify and characterize soft degrees of freedom. Here, we report on the most abundant conformer of ethyl 2-ethyl butyrate using Fourier-transform microwave spectroscopy. We show that - unlike other structurally related pentanoates for which gas-phase and crystallographic data is available - ethyl 2-ethyl butyrate possesses a Cs symmetry plane under molecular jet conditions.

A novel bismuthates(III) complex, (C6H14N)4[BiCl6]Cl·2H2O, was synthesized and characterized by X-ray diffraction and FT-IR spectroscopy. Its structure consists of protonated cyclohexylamine cations, discrete [BiCl6]3− anions, chlorine anions and water molecules. The chlorobismuthate(III) anions alternate with the water molecules O1 as to form hydrogen-bonded helical chain running along the crystallographic b-axis with a period of 17.622 A. These components are connected into a three-dimensional network via hydrogen bonds. In addition, the ground state geometry, vibrational wavenumbers and Natural bond orbital (NBO) analysis were studied by means of density functional theory (DFT/B3LYP) with LanL2DZ basis set. Theoretical results are within the range of the experimental data. The NBO analysis reveals the influence of the N–H…O, N–H…Cl and O H…Cl intermolecular interactions on crystal packing. Moreover, the electrochemical behavior of this complex was investigated in DMSO by cyclic voltammetry (CV).

We present the results of a systematic investigation, at the BHandHLYP/AVTZ density functional (DFT) level, of the tautomeric equilibria of 1,2,3- and 1,2,4-triazoles and their reactions with hydroxyl radicals in the gas phase. A total of twenty-six chemical reactions has been studied, and thermodynamical data and rate constants are reported. The reactions can be classified in two categories: hydrogen abstraction and OH addition. Nine of these reactions are favourable at room temperature. It was found that OH addition proceeds more rapidly than hydrogen abstraction, by several orders of magnitude. For the most stable tautomers, which presumably dominate in the gaz-phase, the fastest reactions are OH addition to 2H-1,2,3-triazole and site-specific OH addition to carbon atom 5 of 1H-1,2,4-triazole. In absolute values, however, the rate constants are rather small, k=5.82×10-20 cm3 s-1 and k=4.75×10-18 cm3 s-1 , respectively, at room temperature. Therefore, under the conditions of the troposphere, triazoles cannot be eliminated by reactions with OH. The accuracy of the computational approach has been demonstrated by studying the tautomeric equilibria of 1,2,3- and 1,2,4-triazoles in the gas phase. The computed equilibrium constants are in excellent agreement with those derived from spectroscopic observations. Additional assessment of the quality of the computed data was made by comparison with the results from high-level CCSD(T)-F12/AVTZ ab initio calculations for three exemplary structures. This comparison demonstrates the high accuracy of our DFT results of 0.29 kcal mol-1 for energy differences between stable isomers.

International audience; Internal rotation is a fundamental motion of end-standing methyl groups that provides important insight on the molecular physics of isolated molecules. The barrier heights of such large amplitude motions are highly sensitive to their molecular and electronic environment. Until now, it is still not possible to accurately determine barrier heights using quantum chemical calculations. To probe for the effect of molecular conformations on the barrier heights of substituted furan rings, the molecular jet Fourier transform microwave spectrum of 5-methyl furfural was recorded in the frequency range from 2 to 40 GHz. Quantum chemical calculations yielded two conformers with a trans and a cis orientation of the formyl group, which were both observed in the experimental spectrum. Torsional splittings due to the internal rotation of the methyl group were resolved and analyzed. The experimental spectra is reproduced with standard deviations close to the experimental accuracy, yielding sets of highly accurate rotational and internal rotation parameters. The results, especially the V3 potentials, are compared to quantum chemical calculations and discussed within the scope of the current literature of other methyl substituted furans, where the methyl group is in close proximity of the furan oxygen atom. Our work provides an accurate evaluation of the different case studies and highlights the bottle necks and future options of current available theoretical techniques.

Dioxygen difluoride is a tough molecule that has defied accurate theoretical description for many decades. In the present work we have identified the reason for this resistance: the flatness of the OO, and more important OF, stretching potential energy curves, which make it difficult to localise the global minimum. It is not related to the weak multi-reference character. Using high-level CCSD(T)-F12/VTZ-F12 ab initio theory, the global minimum has been properly located and vibrationally averaged bond lengths obtained. These vibrationally averaged parameters agree with experimental data to within 0.01 Å. Averaging was found essential to achieve this unprecedented accuracy. We have then simulated the IR and UV spectra, which compare well with experimental data and permit identification of the observed transitions.

A novel Cd(II) coordination polymer [Cd(C4H11N2)(μ-Cl)2Cl] n ·nH2O with a supramolecular structure has been synthesized by reaction of CdCl22·5H2O with piperazine. The compound was investigated by X-ray diffraction, electrochemistry, and IR spectroscopy. The CdCl3(C4H11N2)·H2O entity in the compound forms a 1D coordination polymer as a result of the bridging function of the chlorine atoms Cd–Cl2–Cd. Adjacent 1D coordination polymers are connected by (O,N,C)–H…Cl, (O,N)–H…Cl, and N–H…O hydrogen bonds, generating a three-dimensional supramolecular network. With this atomic arrangement, the complex can form an electroactive film on a platinum electrode by anodic oxidation in acetonitrile solution.

There has been a disagreement amongst experimentalists and between experimentalists and theoreticians as to the gas-phase structure of dimethyl peroxide. We have investigated this problem with high-level CCSD(T)-F12 and MRCI procedures. There can be no doubt anymore that, at the minimum of the potential energy surface, the COOC fragment has a trans-structure. The dynamical structure of the molecule can, however, be different and be explained by the very slow torsional motion. We have analysed the dynamical structure using numerical wavefunctions of the torsional motion and a fully optimized potential curve of MP2/aug-cc-pVTZ quality. Computational and all experimental results are shown to be in complete agreement. The problem that has persisted for more than thirty years, highlighted in a recent review article by Oberhammer titled "Gas phase structures of peroxides: experiments and computational problems", has been resolved.

The in vivo chlorophyll (Chl) fluorescence spectra of Solanum lycopersicum leaves were recorded in the spectral region 650-800nm using a spectroscopic method based on ultraviolet light emitting diode induced fluorescence spectroscopy (UV-LED IFS). These spectra have been used to analyze the interactive functions of cadmium (Cd(2+)) and zinc (Zn(2+)) on photosynthetic activities of S. lycopersicum plants. The fluorescence intensity ratios (F(690)/F(735)) of the chlorophyll bands at 685 and 730nm were calculated by evaluating curve fitted parameters using a Gaussian spectral function, for control as well as treated plants. The fluorescence induction kinetics (Kautsky effect) was also measured on dark adapted intact plant leaves at the chlorophyll bands for determining the variable chlorophyll fluorescence decrease ratio (R(Fd) values) and the stress adaptation index (Ap). In addition, metal accumulation in plants, plant growth and photosynthetic pigments content were estimated. It was found that the R(Fd)(690), R(Fd)(730) and Ap values decreased whereas the F(690)/F(735) ratio increased in the case of 10μM Cd(2+) treated plants, indicating an impairment of the photosynthetic efficiency. Zn(2+) supplementation, at low concentration (10 and 50μM), in combination with Cd(2+) protect the photochemical functions. However, the high Zn(2+) concentration exacerbated the negative effects of Cd(2+) and showed a severe decrease of R(Fd)(690), R(Fd)(730) and Ap values compared to Cd(2+) alone. It is seen that F(690)/F(735) ratios are strongly correlated with chlorophyll contents. The results demonstrate the usefulness of F(690)/F(735), Ap and R(Fd) values in determining the potential photosynthetic activity of an intact attached leaf in a non-destructive way.

Knowledge of the structure of hydrated ions in hydrophobic media is crucial for understanding the mechanism of many biological processes and is relevant to a variety of technological applications. We focus here on the hydrated shell of the K+ cation, which has been widely investigated, both experimentally and theoretically, in gas phase and in aqueous solution. Recent experimental work has also been devoted to investigate Na+ and K+ halides transfer through a water/organic interface suggesting that the traditional view of hydrated ions entering the hydrophobic phase is not valid. We report a quantum mechanical study of K+(H2O)n clusters (n = 1, 8) in gas phase and in dielectric media with dielectric constants e = 2, 10 corresponding to non-polar and low-polar environments, respectively. We show that dielectric effects significantly modify the stability and size of the hydrates. In particular, our computations suggest that in non-polar media, mono- and di-hydrates (n = 1, 2) are the most stable species and that hexahydrates (n = 6) have two water molecules in the second solvation shell.

The electrogeneration of pure 4,4′-di-tert-butylbiphenyl peroxide as an electrodeposit could be achieved on a platinum electrode through the anodic oxidation of p-tert butylphenol in the presence of Lutidine, in addition to several soluble oligomers. The electrochemical and theoretical studies have shown that the favored coupling reaction corresponds to the O–O bond, albeit it is generally being considered unstable. Without the strong base, a mixture of trimer, tetramer and pentamer was deposited. The peroxide product presents a different electroactivity to that of the phenolic compound, with the appearance of a redox process involving cathodic and anodic symmetrical peaks at −0.10/0.15 V versus SCE, which indicates the preference of the polymer to adhere onto the electrode surface. The thermal degradation has also been analyzed. Quantum-chemical calculations reveal the reason for the oxygen–oxygen coupling.

In this work it is shown that, with a new spectroscopic method based on ultraviolet light emitting diode-induced fluorescence spectroscopy (UV-LED IFS), the photosynthetic activity of an intact attached leaf can be measured in a non-destructive way within a few seconds. The effects of cadmium (Cd) toxicity on the photosynthetic activity of tomato plants (Solanum lycopersicum) were studied using various CdCl2 (cadmium chloride) concentrations. The Cd treatment decreases the photosynthetic activity, measured via a decline of the variable chlorophyll (chl) fluorescence decrease ratio (RFd) values, calculated at 690 and 730 nm. The chl fluorescence ratios of intensity (FIR) and band area were also calculated. It was found that the RFd(690) and RFd(730) values decreased whereas the FIR increased from 1 μM Cd treatment and this behaviour is enhanced with the increasing of Cd concentrations. At 10 and 25 μM Cd, the decrease in RFd values was associated with a strong decline in the chlorophyll-a + chlorophyll-b (chl-a + b). The chl-a + b decline could also be followed via an increase of the chl fluorescence ratio F690/F730. Our study demonstrates that the UV-LED IFS is a promising technique for early detection of Cd stress (from 1 μM) in tomato plants, before visual symptoms appear.

A systematic study on the magnetic property variations of Pd13 particles as a function of particle sizes and structures, and of Pd13 interactions with the (100) TiO2 anatase surface, was carried out with standard density functional theory (DFT) based method with periodic boundary conditions. The biplanar Pd13 structure with the spin state quintet is obtained to be the ground state in the gas-phase and on the anatase surface, being more stable than the compact icosahedral configuration by 0.067 and 0.865 eV, respectively. The preferred particle nucleation on the anatase surface is that with the largest possible contacts between Pd13 and the oxide surface oxygens. The supported Pd13 particles are better stabilized by 0.3 eV compared to the isolated ones. The profiles of the relative energies as a function of the spin state reveal that the Pd13 magnetic isomers, belonging to the same cluster topology, become closer in energy and nearly degenerate on the anatase surface compared to their gas-phase counterpart...

An investigation of the elastic properties of hexagonal phases of typical liquid crystal samples on an ordered hexagonal discotic hexa-n-octyloxytriphenylene (C 8 HET), a disordered one a triphenylene hexa-n-dodecanoate (C 11 HAT) and a hexacatenar phasmid was carried out. Characterization of their mechanical stability and analysis of light scattering were used; the same results were obtained for the three samples in spite of the differences in their molecular shapes and molecular orders in columns. From the instability of undulating columns submitted to a dilative strain normal to columns, we deduced an anomalously large value of the correlation length m (m ≃ 0.1 μm), compared to that of the smectic liquid crystals (m ≃ 20 A). Results from depolarized Rayleigh scattering showed that, although consisting of one-dimensional liquid-like structures, the studied samples in their hexagonal phases behaved elastically like three-dimensional solids. Considering the differences in molecular shapes and orders, this elastic behaviour was attributed to regular defects. Therefore, one can probably generalize this elastic behaviour as being due to the columnar hexagonal structure.

We have investigated 'hexa- n -alcanoyloxytruxene' HATXC H which exhibits a disk-like thermotropic nematic phase between 65 and 84 C. Using a light-beating technique we have measured the orientational diffusivities D a correspond respectively to twist and bend deformations. D twist increases monotonically as temperature increases, while D remains constant. This result means that the curvature bend elastic constant K changes more rapidly than the viscosity eta 22 in the same ratio. This means also that in the discotic thermotropic nematic phase, when temperature increases the effective hydrodynamic object, in orientational fluctuation, changes shape to be disk-like rather than rod-like. 9 19 nd D for several temperatures, which twist bend, while K and eta change twist 33 bend

We analyze the structure, hydration, and pK(a) values of p-guanidinoethyl-phenol through a combined experimental and theoretical study. These issues are relevant to understand the mechanism of action of the tetrameric form, the antibacterial compound tetra-p-guanidinoethyl-calix[4]arene (Cx1). The investigated system can also be useful to model other pharmaceutical drugs bearing a guanidine function in the vicinity of an ionizable group and the effect of arginine on the pK(a) of vicinal ionizable residues (in particular tyrosine) in peptides. The p-guanidinoethyl-phenol monomer (mCx1) has two ionizable groups. One important particularity of this system is that it exhibits high molecular flexibility that potentially leads to enhanced stabilization in folded structures by direct, strong Coulombic interactions between the ionizable groups. The first pK(a) corresponding to ionization of the -OH group has experimentally been shown to be only slightly different from usual values in substituted phenols. However, because of short-range Coulombic interactions, the role of intramolecular interactions and solvation effects on the acidities of this compound is expected to be important and it has been analyzed here on the basis of theoretical calculations. We use a discrete-continuum solvation model together with quantum-mechanical calculations at the B3LYP level of theory and the extended 6-311+G(2df,2p) basis set. Both intra- and intermolecular effects are very large (~70 kcal/mol) but exhibit an almost perfect compensation, thus explaining that the actual pK(a) of mCx1 is close to free phenol. The same compensation of environmental effects applies to the second pK(a) that concerns the guanidinium group. Such a pK(a) could not be determined experimentally with standard titration techniques and in fact the theoretical study predicts a value of 14.2, that is, one unit above the pK(a) of the parent ethyl-guanidinium molecule.

The effects of zinc (Zn) on plant chlorophyll fluorescence were investigated in 10-day-old tomato ( Solanum lycopersicum ) seedlings subjected for 7 days to a series of zinc (10, 50, 100 and 150 μM) applied via the nutrient solution. The chlorophyll fluorescence spectra of leaves were recorded in the spectral region 650–800 nm using the spectroscopic technique of ultraviolet light emitting diode induced fluorescence spectroscopy (UV-LED IFS). These spectra have been used to analyze the effect of several doses of zinc on the photosynthetic activities of tomato plants. The fluorescence intensity ratios (FIR) at the two maxima ( F 690 / F 735 ) of control as well as treated tomato plants were calculated by evaluating curve-fitted parameters using a Gaussian spectral function. The variable chlorophyll fluorescence decrease ratio ( R Fd ) values were determined from the fluorescence induction kinetics curves recorded at 690 nm and 735 nm. In addition, Zn accumulation in plants, plant growth, photosynthetic pigments content and malondialdehyde level (MDA, an index of lipid peroxidation) were also estimated. The results indicated that the plants treated with 10 μM of zinc exhibited better growth, however, higher concentrations of zinc were harmful for plants. Excess Zn induced a decrease in the R Fd values, which was associated with a strong decline of the total chlorophylls content and an increase of MDA level. The total chlorophylls content decline could also be followed via an increase of the chlorophyll fluorescence ratio F 690 / F 735 .

In two recent reports of the same series (J. Phys. Chem. B 2007, 111, 1470-1477 and J. Phys. Chem. B 2009, 113, 3169-3178), we have described the geometrical and vibrational analysis of glycine and amino acids (AAs) with hydrophobic side chains through the joint use of optical spectroscopy and quantum mechanical calculations. Here, we report Raman scattering and Fourier-Transform Infrared (FT-IR) Attenuated Total Reflectance (ATR) spectra measured from the aqueous solutions (H(2)O and D(2)O) of L-lysine and L-arginine, i.e. two alpha-AAs with positively charged hydrophilic side chains. The discussion on the vibrational features of both AAs could be carried out thanks to the theoretical calculations performed by means of the Density Functional Theory (DFT) approach at the B3LYP/6-31++G* level. We have analyzed the influence of implicit (with a polarizable dielectric continuum) and explicit (by means of an H(2)O cluster interacting with H-donor and H-acceptor sites of AAs) hydration models. In addition, through the calculated geometrical parameters and vibrational wavenumbers, a discussion was performed on the effect of the Cl(-) anion interacting with the positively charged side chains of explicitly hydrated AAs.

1 - Article; Raman scattering and Fourier-transform infrared (FT-IR) attenuated transmission reflectance (ATR) spectra of two alpha-amino acids (alpha-AAs), i.e., glycine and leucine, were measured in H2O and D2O (at neutral pH and pD). This series of observed vibrational data gave us the opportunity to analyze vibrational features of both AAs in hydrated media by density functional theory (DFT) calculations at the B3LYP/6-31++G* level. Harmonic vibrational modes calculated after geometry optimization on the clusters containing each AA and 12 surrounding water molecules, which represent primary models for hydration scheme of amino acids, allowed us to assign the main observed peaks.

Science Development leads to new concepts, new tools and new techniques. It leads to a society development with new Truth. This Truth is shared by the Society which development is built on Knowledge, on rationality thinking and scientific behavior. This takes its origin in the experimental approach introduced by Ibn Al Haythem in optics at the Xth century.By the end of the last millennium, this approach-known as Active Learning in Physics- has been adopted in most developed countries in physics education programs. Active Learning in Optics and Photonics- ALOP- is extended actually to some developing countries through a UNESCO program.A French edition of ALOP takes place through many workshops over Morocco and Tunisia. It aims to build Truth on evidence and not on intuition or personal authority.