Search results for "ethane"
showing 10 items of 2342 documents
Theoretical investigation of the spin crossover transition states of the addition of methane to a series of Group 6 metallocenes using minimum energy…
2016
International audience; Density functional calculations are reported on the addition of methane to Group 6 metallocenes, M(η-C5H5)2 (M), M(CH2(η-C5H4)2) (a-M) and M(η-C5Me5)2 (M*) where M = Mo and W. Full geometry optimisations were carried out on the singlet and triplet 16 electron complexes, 1[M] and 3[M], the η2-methane complexes, 1[M(η2-CH4)], and the hydridomethyl adducts, 1[M(CH3)(H)]. The triplet state for [M] was found to be more stable for all six metallocenes, the difference being least in the case of the ansa-bridged system. Formation of the hydridomethyl complexes was exoenergetic for all tungsten systems and for a-Mo, the other two Mo systems being endoenergetic. Minumum energy…
A novel comprehensive procedure for estimating greenhouse gas emissions from water resource recovery facilities
2017
The emissions of the major greenhouse gases (GHGs), i.e. carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) from water resource recovery facilities (WRRFs) are of increasing concern in the water industry. In order to produce useful and comparable information for monitoring, assessing, and reporting GHG emissions from WRRFs, there is a need for a generally accepted methodology for their quantification. This paper aims at proposing the first protocol for monitoring and accounting for GHG emissions from WRRFs, taking into account both direct and indirect internal emissions and focusing the attention on plant sections known to be primarily responsible for GHG emissions (i.e. oxidation…
The high-resolution far-infrared spectrum of methane at the SOLEIL synchrotron
2010
International audience; As a tetrahedral molecule, methane has no permanent dipole moment. Its spectrum, however, displays faint absorption lines in the THz region, due to centrifugal distorsion effects. This is important for planetary applications since this region is used to measure methane concentration in some planetary atmospheres, in particular on Titan. Up to now, all measurements relied either on some old low resolution infrared absorption spectra, or on high resolution Stark measurements for low J values only. Even if these results have been reexamined recently [E. H. Wishnow, G. S. Orton, I. Ozier and H. P. Gush, J. Quant. Spectrosc. Radiat. Transfer 103, 102-117 (2007)], it seeme…
A record of seafloor methane seepage across the last 150 million years
2020
<p>Methane seepage at the seafloor is a source of carbon in the marine environment and has long been recognized as an important window into the deep geo-, hydro-, and bio-spheres. However, the processes and temporal patterns of natural methane emission over multi-million-year time scales are still poorly understood. The microbially-mediated methane oxidation leads to the precipitation of authigenic carbonate minerals within subseafloor sediments, thus providing a potentially extensive record of past methane emission. In this study, we used data on methane-derived authigenic carbonates to build a proxy time series of seafloor methane emission over the last 150 My. We quantitat…
Applications of a new set of methane line parameters to the modeling of Titan's spectrum in the 1.58 μm window
2012
International audience; In this paper we apply a recently released set of methane line parameters (Wang et al., 2011) to the modeling of Titan spectra in the 1.58 mu m window at both low and high spectral resolution. We first compare the methane absorption based on this new set of methane data to that calculated from the methane absorption coefficients derived in situ from DISR/Huygens (Tomasko et al., 2008a; Karkoschka and Tomasko, 2010) and from the band models of Irwin et al. (2006) and Karkoschka and Tomasko (2010). The Irwin et al. (2006) band model clearly underestimates the absorption in the window at temperature-pressure conditions representative of Titan's troposphere, while the Ka…
Abiotic and biotic controls on methane formation down to 2.5 km depth within the Precambrian Fennoscandian Shield
2017
Abstract Despite a geological history characterised by high temperature and pressure processes and organic carbon deprived crystalline bedrock, large amounts of hydrocarbons are found in deep groundwaters within Precambrian continental shields. In many sites, methane comprises more that 80% of the dissolved gas phase reaching concentrations of tens of mmol l −1 . In this study, we used isotopic methods to study the carbon isotope systematics and sources of crustal methane within the Fennoscandian Shield. The main study sites were the Outokumpu Deep Drill Hole and the Pyhasalmi mine in Finland, both of which allow groundwater sampling down to 2.5 km depth and have been previously studied for…
Water vapor increase in the northern lower stratosphere by the Asian monsoon anticyclone observed during TACTS/ESMVal campaigns
2017
Abstract. The impact of air masses from Asia influenced by the Asian monsoon anticyclone on the northern hemispheric stratosphere is investigated based on in-situ measurements. An statistical significant increase in water vapor of about 0.5 ppmv (11 %) and methane up to 20 ppbv (1.2 %) in the extra-tropical stratosphere above a potential temperature of 380 K was detected between August and September 2012 by in-situ instrumentation in the northern hemisphere during the HALO aircraft mission TACTS and ESMVal. We investigate the origin of this water vapor and methane increase with the help of the three-dimensional Lagrangian chemistry transport model CLaMS. We assign the source of the moist ai…
Titan's surface albedo variations over a Titan season from near-infrared CFHT/FTS spectra
2006
International audience; We have observed Titan in a series of campaigns from 1991 to 1996 with the Fourier Transform Spectrometer on the CFH telescope. The data acquired provide a lightcurve from the geometric albedos in the 0.9–View the MathML source spectral region. The 1991–1993 data were previously analyzed in Coustenis et al. [1995. Titan's surface: composition and variability from its near-infrared albedo. Icarus 118, 87–104] with a spherical particle code by McKay et al. [1989. The thermal structure of Titan's atmosphere. Icarus 80, 23–53]. We present here three new datasets from the 1994, 1995 and 1996 observations, with additional information from the 0.94-μm methane window on Tita…
Methanotrophy in geothermal soils, an overlooked process: The example of Nisyros island (Greece)
2020
Abstract A multidisciplinary field campaign was carried out at Nisyros Island (Greece). Hydrothermal gases were sampled and analysed, and CH4 and CO2 fluxes from the soils were measured with the accumulation chamber method. The sampling area (Lakki plain) covers an area of about 0.08 km2, and includes the main fumarolic areas of Kaminakia, Stefanos, Ramos, Lofos and Phlegeton. Flux values measured at 130 sites range from −3.4 to 1420 mg m−2 d−1 for CH4 and from 0.1 to 383 g m−2 d−1 for CO2. The fumarolic areas show very different CH4 degassing patterns, Kaminakia showing the highest CH4 output values (about 0.8 t a−1 from an area of about 30,000 m2) and Phlegeton the lowest (about 0.01 t a−…
Line parameters and shapes of high clusters: R-branch of the nu3 band of CH4 in He mixtures
2002
International audience; The IR absorption spectra of CH4 in pure gas and in mixture with helium were studied in the region of nu3 band at higher J line clusters R(17)-R(22). The frequencies and intensities of rotation-vibration lines were estimated from the experimental spectra at Doppler shape conditions. The line frequencies and intensities were calculated and used for the attribution of overlapped lines in clusters. The calculated line intensities are close to the experimental values. The calculated frequency structure of the higher J manifolds are somewhat wider than the observed one. The shapes of helium-broadened line clusters were compared with those calculated accounting for line mi…