Unusual polymerization in the Li4C60 fulleride

Li4C60, one of the best representatives of lithium intercalated fullerides, features a novel type of 2D polymerization. Extensive investigations, including laboratory x-ray and synchrotron radiation diffraction, 13C NMR, MAS and Raman spectroscopy, show a monoclinic I2/m structure, characterized by chains of [2+2]-cycloaddicted fullerenes, sideways connected by single C-C bonds. This leads to the formation of polymeric layers, whose insulating nature, deduced from the NMR and Raman spectra, denotes the complete localization of the electrons involved in the covalent bonds.Comment: 7 pages, 6 figures, RevTex4, submitted to Phys. Rev.

Agronomical and analytical trait data assessed in a set of quinoa genotypes growing in the UAE under different irrigation salinity conditions

The importance of quinoa has been emphasized considerably in the recent decades, as a highly nutritional crop seed that is tolerant to salinity and amenable to arid agronomical conditions. The focus of this paper is to provide raw and a supplemental data of the research article entitled "Agronomic performance of irrigated quinoa in desert areas: comparing different approaches for early assessment of salinity stress" [1], aiming to compare different approaches for early detection, at the genotypic and crop levels, of the effect of salinity caused by irrigation on the agronomic performance of this crop. A set of 20 genotypes was grown under drip irrigation in sandy soil, amended with manure, at the International Center for Biosaline Agriculture (UAE) for two weeks, after which half of the trial was submitted to irrigation with saline water and this was continued until crop maturity. After eight weeks of applying the two irrigation regimes, pigment contents were evaluated in fully expanded leaves. The same leaves were then harvested, dried and the stable carbon and nitrogen isotope compositions (δ13C and δ15N) and the total nitrogen and carbon contents of the dry matter analyzed, together with ion concentrations. At maturity yield components were assessed and yield harvested. Data analysis demonstrated significant differences in genotypes response under each treatment, within all assessed parameters. The significant level was provided using the Tukey-b test on independent samples. The present dataset highlights the potential use of different approaches to crop phenotyping and monitoring decision making

A study of structural phase transitions by infrared spectroscopy of vibrational excitons: application to crystalline phenothiazine

International audienceInfrared spectroscopy of vibrational excitons is a good method to study the second order structural phase transitions which are observed in some molecular crystals. Crystalline phenothiazine (C/sub 12/H/sub 9/NS) undergoes such a transition at about T/sub c/=250 K from a high-temperature orthorhombic phase with a space group Pbnm (D/sub 2h//sup 16/) to a low-temperature monoclinic phase with a space group P2/sub 1//n (C/sub 2h//sup 5/). This transition is studied by infrared spectroscopy of two bands at 426 cm/sup 1/ (A" mode) and at 925 cm/sup -1/ (A' mode). The splitting of the exciton components of these bands is studied as a function of temperature and can be described by a (T/sub c/-T)/sup beta / law with a critical exponent beta of an approximate value of 0.45. This result agrees with Landau's theory of second order phase transitions

VO₂ thin films for smart windows: Numerical study of the optical properties and performance improvement

Abstract Vanadium dioxide (VO2) have attracted tremendous interest in recent years due to their semiconductor-metal transition near room temperature. In this work, we report numerical simulation of the optical properties of VO2 thin layers which include the index of refraction, the coefficient of extinction, the reflectance and the transmittance. In this sense, we used the Model of Drude-Lorentz for calculating coefficients at from the optical parameters n and k using the determination of the dielectric constant ε (ω, T). Knowing that the semiconductor-metal transition temperature of VO2 is 68 °C, the thickness effect on the optical properties of VO2 thin films has been studied by transmittance simulations. Our results revealed a significant changes in optical properties of VO2 thin layers, which produces many interesting applications especially for smart windows.</jats:p