Search results for "Spectra"
showing 10 items of 3542 documents
Structural and spectroscopic characterisation of 2-(2'-hydroxybenzoyl)pyrrole and its O-methyl derivative
2004
Abstract Density functional theory calculations on the tautomeric and conformational equilibria of 2-(2′-hydroxybenzoyl)pyrrole (HBP) and 2-(2′-methoxybenzoyl)pyrrole (MBP) were performed. Moreover, the experimental IR and UV spectra of the same compounds were recorded and compared with the theoretical data. The presence of an intramolecular hydrogen bond in HBP can be related to the biological activities of some of its derivatives.
Deuterium hyperfine splittings in the rotational spectrum of NH2D as revealed by Lamb-dip spectroscopy
2020
Abstract In the context of radio-astronomical observations, laboratory experiments constitute a cornerstone in the interpretation of rich line surveys due to the concomitant presence of numerous emitting molecules. Here, we report the investigation of three different rotational transitions of mono-deuterated ammonia (NH2D), a species of astrophysical interest, for which the contribution of the deuterium nuclear spin to the rotational spectrum has been resolved for the first time in the millimeter- and submillimeter-wave domain. The effect of hyperfine interactions on the rotational spectrum has been unveiled by a combined theoretical and experimental approach. Quantum-chemical calculations …
15N NMR: Substituent effect analysis inpara-andmeta-substituted phenylhydrazines
1994
15N NMR spectra of phenylhydrazine and of 14 para- and meta-substituted phenylhydrazines were measured at natural isotope abundance in DMSO-d6 solution. The substituent present exerts a larger influence on the chemical shift of the nitrogen atom directly bound to the aromatic ring (N-1) than on the second one (N-2), which shows an attenuated and inverted trend. The chemical shifts of N-1 and N-2 give a good cross correlation in both series of compounds if p-NO2 and m-F derivatives are excluded from the correlations of para- and meta-substituted phenylhydrazines, respectively. Moreover, N-1 SCS values show good linear correlations with Hammett substituent constants, with SCSs of directly bou…
Long-term X-ray variability of the microquasar system LS 5039/RX J1826.2−1450
2003
We report on the results of the spectral and timing analysis of a BeppoSAX observation of the microquasar system LS 5039/RX J1826.2-1450. The source was found in a low-flux state with Fx(1-10 keV)= 4.7 x 10^{-12} erg cm^{-2} s^{-1}, which represents almost one order of magnitude lower than a previous RXTE observation 2.5 years before. The 0.1--10 keV spectrum is described by an absorbed power-law continuum with photon-number spectral index Gamma=1.8+-0.2 and hydrogen column density of NH=1.0^{+0.4}_{-0.3} x 10^{22} cm^{-2}. According to the orbital parameters of the system the BeppoSAX observation covers the time of an X-ray eclipse should one occur. However, the 1.6-10 keV light curve does…
Application of 61Ni Mössbauer spectroscopy to chemical problems
1996
Using the possibility to produce 61Co sources at the MAinz MIcrotron, 61Ni Mossbauer spectroscopy was applied to different kinds of chemical problems. Measurements of isomer shifts and V zz values in some common compounds and compounds with unusual chemical bonding for comparison with band structure calculations, measurement of 61Ni Mossbauer parameters in model compounds for hydrogenase and dehydrogenase with an active [NiS4] centre, and study of novel binary NiF3 compounds at helium temperature are presented.
Estimation of Evapotranspiration by Hargreaves Formula and Remotely Sensed Data in Semi-arid Mediterranean Areas
1997
Abstract A methodology is proposed for estimating evapotranspiration by Hargreaves formula and image analysis of remotely sensed data. At first, for a large sicilian basin (Belice basin), theactualevapotranspiration values are estimated by the energy balance equation, spectral data of two Landsat TM images and ground agrometereological measurements. Then theseactualevapotranspiration estimates and thereferenceevapotranspiration values obtained by a slightly modified Hargreaves formula, which incorporates the outgoing short-wave radiation and an albedo coefficient equal to 0·23, are used for calculating suitable crop coefficients. Finally, the minimum area of each land-use map unit, obtained…
Detecting crop water status in mature olive orchards using vegetation spectral measurements.
2014
Full spectral measurements (350–2500 nm) at tree canopy and leaf levels and the corresponding leaf water potentials (LWP) were acquired in an olive grove of Sicily, at different hours of the day, during summer season 2011. The main objective of the work was to assess, on the basis of the experimental data-set, two different approaches to detect crop water status in terms of LWP. Specifically, using existing families of Vegetation Indices (VIs) and applying Partial Least Squares Regression (PLSR) were optimised and tested. The results indicated that a satisfactory estimation of LWP at tree canopy and leaf levels can be obtained using vegetation indices based on the near infrared–shortwave in…
Vegetation cover seasonal changes assessment from TM imagery in a semi-arid landscape
2004
This work evaluates the suitability of spectral mixture analysis (SMA) methods to assess vegetation cover seasonal changes in a desertification context. Our main interest is to produce remotely sensed derived maps, sensitive to vegetation activity and quite independent of the soil background. A further aim is to analyse the inter-annual variations of this magnitude for different natural vegetation species, in response to seasonal and climatic changes. Fractional vegetation cover (FVC) was obtained using a Variable Endmember Spectral Mixture Analysis (VESMA) technique. The aim is to identify the main vegetation cover and lithological units and decompose them in separate stages. The use of sp…
Recent results on mesonic weak decay of Λ-hypernuclei
2010
The FINUDA experiment has performed a systematic study of mesonic weak decay of p-shell Λ-hypernuclei. Recent results on the mesonic decay spectra and ratios are illustrated and discussed.
Strong thermal nonequilibrium in hypersonic CO and CH4 probed by CRDS
2015
A new experimental setup coupling a High Enthalpy Source (HES) reaching 2000 K to a cw-cavity ring-down spectrometer has been developed to investigate rotationally cold hot bands of polyatomic molecules in the [1.5, 1.7] μm region. The rotational and vibrational molecular degrees of freedom are strongly decoupled in the hypersonic expansion produced by the HES and probed by cavity ring-down spectroscopy. Carbon monoxide has been used as a first test molecule to validate the experimental approach. Its expansion in argon led to rotational and vibrational temperatures of 6.7 ± 0.8 K and 2006 ± 476 K, respectively. The tetradecad polyad of methane (1.67 μm) was investigated under similar condit…