Towards an effective potential for the monomer, dimer, hexamer, solid and liquid forms of hydrogen fluoride

We present an attempt to build up a new two-body effective potential for hydrogen fluoride, fitted to theoretical and experimental data relevant not only to the gas and liquid phases, but also to the crystal. The model is simple enough to be used in Molecular Dynamics and Monte Carlo simulations. The potential consists of: a) an intra-molecular contribution, allowing for variations of the molecular length, plus b) an inter-molecular part, with three charged sites on each monomer and a Buckingham "exp-6" interaction between fluorines. The model is able to reproduce a significant number of observables on the monomer, dimer, hexamer, solid and liquid forms of HF. The shortcomings of the model are pointed out and possible improvements are finally discussed.Comment: LaTeX, 24 pages, 2 figures. For related papers see also http://www.chim.unifi.it:8080/~valle

The Herschel-Heterodyne Instrument for the Far-Infrared (HIFI)

Aims. This paper describes the Heterodyne Instrument for the Far-Infrared (HIFI) that was launched onboard ESA's Herschel Space Observatory in May 2009. Methods. The instrument is a set of 7 heterodyne receivers that are electronically tuneable, covering 480–1250 GHz with SIS mixers and the 1410–1910 GHz range with hot electron bolometer (HEB) mixers. The local oscillator (LO) subsystem comprises a Ka-band synthesizer followed by 14 chains of frequency multipliers and 2 chains for each frequency band. A pair of auto-correlators and a pair of acousto-optical spectrometers process the two IF signals from the dual-polarization, single-pixel front-ends to provide instantaneous frequency coverage of 2 × 4 GHz, with a set of resolutions (125 kHz to 1 MHz) that are better than 0.1 km s^(-1). Results. After a successful qualification and a pre-launch TB/TV test program, the flight instrument is now in-orbit and completed successfully the commissioning and performance verification phase. The in-orbit performance of the receivers matches the pre-launch sensitivities. We also report on the in-orbit performance of the receivers and some first results of HIFI's operations

Archaeometrical study of Khmer stoneware from the Angkorian period: Results from the Cerangkor Project

In the area around Angkor, Cambodia, several ceramics kilns dating from the ninth to 15th centuries ce have been discovered since 1995. The technical, typological and compositional characterization of their production has been one of the main goals of the Cerangkor Project. Samples of green‐glazed ‘Kulen‐type' stoneware and non‐ glazed stoneware produced in five kiln sites in the Angkor region were analysed chemically by wavelength‐dispersive X‐ray fluorescence spectrometry (WDS‐XRF) and also petrographically. The data indicate that some workshops used similar raw materials for the same types of ceramics, suggesting the exploitation of the same geological formations in the whole region. Several references groups were established for each type of stoneware offering an important database for future provenance studies of sherds from consumption sites

Archaeometrical study of Khmer stoneware from the Angkorian period: Results from the Cerangkor Project

International audienceIn the area around Angkor, Cambodia, several ceramics kilns dating from the ninth to 15th centuries CE have been discovered since 1995. The technical, typological and compositional characterization of their production has been one of the main goals of the Cerangkor Project. Samples of green-glazed 'Kulen-type' stoneware and non-glazed stoneware produced in five kiln sites in the Angkor region were analysed chemically by wavelength-dispersive X-ray fluorescence spectrometry (WDS-XRF) and also petrographically. The data indicate that some workshops used similar raw materials for the same types of ceramics, suggesting the exploitation of the same geological formations in the whole region. Several references groups were established for each type of stoneware offering an important database for future provenance studies of sherds from consumption sites

Spectroscopie PM-IRRAS d'un cristal liquide de 9CB déposé en couches minces sur un substrat métallique

Nous présentons une analyse quantitative des spectres de réflectivité différentielle infrarouge (PM-IRRAS) d'un cristal liquide (9CB) déposé en couches ultra-minces sur un substrat d'or. La comparaison entre les intensités mesurées sur les spectres PM-IRRAS et le spectre d'absorbance du composé massique permet de déterminer l'orientation et la conformation des molécules de 9CB par rapport au substrat métallique. En particulier, à partir des spectres de la phase cristalline à température ambiante, nous avons trouvé une inclinaison de 35° de l'axe principal de la molécule par rapport à la normale au substrat et mis en évidence une rotation d'ensemble de la chaîne alkyle autour de cet axe principal

Spectroscopie PM-IRRAS d'un cristal liquide de 9CB déposé en couches minces sur un substrat métallique

La spectroscopie de réflectivité différentielle infrarouge par modulation de polarisation (PM-IRRAS) a été utilisée pour obtenir les spectres vibrationnels d'un cristal liquide de 4-nonyl-4'-cyanobiphényle (9CB) déposé en films minces sur substrat d'or. Pour des épaisseurs allant de 1000 à 20 Å les spectres de ces couches minces présentent, dans les différentes phases, des modifications notables par rapport aux spectres correspondants d'un échantillon massique. Après dépôt, le cristal liquide est dans une phase particulière et une trempe à l'azote liquide est nécessaire pour l'amener dans la phase cristalline. Les températures de transition de phase observées sont plus basses que celles du composé massique. Dans le cas de la phase cristalline, les intensités relatives mesurées sur les spectres PM-IRRAS des films minces diffèrent de celles du spectre d'absorbance du composé massique. Ces différences sont liées à une orientation moléculaire spécifique du cristal liquide en couche mince