1,721,005 research outputs found
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
The conformational behaviour of the odorant dihydrocarveol
Full text linkThe odorant dihydrocarveol (CHO) has been investigated in the gas phase using a 2-8 GHz chirped-pulse Fourier transform microwave spectrometer. Dihydrocarveol was purchased as a mixture of n-, iso-, neo-, and neoiso- isomers. The sample was placed in a bespoke heating nozzle at about 85C and seeded in Ne at 5 bar. Three conformers were observed and their rotational constants were determined. By comparing the experimental rotational constants with those calculated ab initio the three conformers were identified as belonging to n-dihydrocarveol. In all three conformers the isopropenyl group is in equatorial position with respect to the six-membered ring, and the OH group maintains the same configuration. The conformers differ in the orientation of the isopropenyl group.Made available in DSpace on 2017-01-26T21:36:52Z (GMT). No. of bitstreams: 3
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Previous issue date: 2016-06-2
Revealing The Chemistry Of Polycyclic Aromatic Hydrocarbons By Plasma Sources
Full text linkDetected through the aromatic infrared bands (3-20 m), polycyclic aromatic hydrocarbons (PAHs) are considered to lock up a large fraction of the carbon in the interstellar medium (ISM) and to significantly impact its physics and chemistry. Despite their importance, much is unknown about their formation and reactivity under the harsh conditions of the ISM.
We are looking at the reactivity of these molecules in the laboratory by means of an electrical discharge nozzle coupled with chirped-pulse Fourier transform microwave (CP-FTMW) spectroscopy in the 2-12 GHz frequency range. Under such energetic conditions, PAHs are expected to undergo fragmentation processes and/or a recombination chemistry. The formed species are then unambiguously identified via their unique microwave signature.
Herein, we present our results obtained from discharge experiments on the PAHs naphthalene (CH) and phenanthrene (CH), both pure and in mixture with acetonitrile (CHCN), a simple nitrogen-containing interstellar molecule. An interesting chemistry has been observed for the investigated PAHs, which will be compared and discussed.Made available in DSpace on 2021-09-24T21:09:48Z (GMT). No. of bitstreams: 2
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Previous issue date: 2021-06-2
TOWARDS UNRAVELLING THE FORMATION OF ICE GRAINS: THE PHENANTHRENE-WATER COMPLEX
No full textPolycyclic aromatic hydrocarbons (PAHs) are believed to act as catalysts in ice grains formation. The formation of interstellar ice can thus be described as an aggregation process of gaseous water starting on PAH surfaces.
The structural investigation of PAH-HO clusters, therefore, represents a first and important step to undertake in order to shed light on potential ice grains formation pathways. Previous studies have focused on mimicking the initial stage of this aggregation process in laboratories by forming complexes between PAH and water molecules in the gas phase and investigating them by microwave spectroscopy. As the outcome of these studies, precise information on the structure and intermolecular interactions were obtained [1,2].
Herein we take this approach further and present preliminary data on the structural investigation of the complex of phenanthrene, a PAH molecule featuring three fused benzene rings, and water. Its pure rotational spectrum was recorded using a chirped pulse Fourier transform microwave spectrometer (CP-FTMW) operating in the region 2-8 GHz, and structural information on the respective water clusters can be obtained.\\
[1] Pérez, C.; Steber, A. L.; Rijs, A. M.; Temelso, B.; Shields, G. C.; Lopez, J. C.; Kisiel, Z.; Schnell, M., Phys. Chem. Chem. Phys. 2017, 19, 14214-14223.
[2] Steber, A. L.; Pérez, C.; Temelso, B.; Shields, G. C.; Rijs, A. M.; Pate, B. H.; Kisiel, Z.; Schnell, J. Phys. Chem. Lett. 2017, 8, 5744-5750
Towards unravelling the formation of ice grains: The phenanthrene-water complex
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Previous issue date: 6Polycyclic aromatic hydrocarbons (PAHs) are believed to act as catalysts in ice grains formation. The formation of interstellar ice can thus be described as an aggregation process of gaseous water starting on PAH surfaces. The structural investigation of PAH-H2O clusters, therefore, represents a first and important step to undertake in order to shed light on potential ice grains formation pathways. Previous studies have focused on mimicking the initial stage of this aggregation process in laboratories by forming complexes between PAH and water molecules in the gas phase and investigating them by microwave spectroscopy. As the outcome of these studies, precise information on the structure and intermolecular interactions were obtained [1,2].
Herein we take this approach further and present preliminary data on the structural investigation of the complex of phenanthrene, a PAH molecule featuring three fused benzene rings, and water. Its pure rotational spectrum was recorded using a chirped pulse Fourier transform microwave spectrometer (CP-FTMW) operating in the region 2-8 GHz, and structural information on the respective water clusters can be obtained.
[1] Perez, C.; Steber, A. L.; Rijs, A. M.; Temelso, B.; Shields, G. C.; Lopez, J. C.; Kisiel, Z.; Schnell, M., Phys. Chem. ´ Chem. Phys. 2017, 19, 14214-14223. [2] Steber, A. L.; Perez, C.; Temelso, B.; Shields, G. C.; Rijs, A. M.; Pate, B. H.; ´ Kisiel, Z.; Schnell, J. Phys. Chem. Lett. 2017, 8, 5744-5750
EXPLORING THE FORMATION OF SILICON-CONTAINING PAH-LIKE MOLECULES IN THE ELECTRICAL DISCHARGE OF PHENYLSILANE AND NAPHTHALENE
Full text linkSilicon is among the most abundant elements in interstellar environments, being only one order of magnitude less than C, N, and O. More than 15 gas-phase silicon bearing molecules have been already detected and a large fraction of silicon is considered to be locked up in interstellar dust grains, where also polycyclic aromatic hydrocarbons (PAHs) are a major constituent. Due to its abundance, silicon can represent an important player in the chemical evolution of the interstellar medium and, in particular, in many interstellar PAHs formation zone. Because of its chemical analogy with carbon, both are tetravalent atoms that form primarily covalent bonds, silicon could substitute either within or on the carbon skeleton of a PAH under the energetic conditions of the ISM, and silicon-substituted PAHs could represent promising candidates for future astronomical searches. In the laboratory, one way to study the make-up of silicon containing PAH-like molecules is by combining cutting-edge spectroscopic techniques with plasma sources. In this work, we used molecular beam mass-selective IR spectroscopy with the free-electron laser FELIX and quantum-chemical calculations to analyze the electrical discharge of phenylsilane and naphthalene. A variety of molecular species resulting from the combination of the precursors were identified via their mass and their IR spectra. The analysis of the latter could help elucidate the influence of Si on the IR spectra of PAHs
The Shapes of Sulfonamides: A Rotational Spectroscopy Study
Full text linkBenzenesulfonamides are a class of molecules of extreme interest in the biochemical field because many of them are active against a variety of diseases. In this work, the pharmacophoric group benzensulfonamide, its derivatives para-toluensulfonamide and ortho-toluensulfonamide, and the bioactive molecule sulfanilamide, were investigated using rotational spectroscopy to determine their conformations and the influence of different substituents on their structures. For all species, the hyperfine structure due to the (14)N atom was analyzed, and this provided crucial information for the unambiguous identification of the observed conformation of all molecules. In addition, for ortho-toluensulfonamide, the vibration–rotation hyperfine structure related to the methyl torsion was analyzed, and the methyl group rotation barrier was determined. For benzensulfonamide, partial r(S) and r(0) structures were established from the experimental rotational constants of the parent and two deuterated isotopic species. In all compounds except ortho-toluensulfonamide, the amino group of the sulfonamide group lies perpendicular to the benzene plane with the aminic hydrogens eclipsing the oxygen atoms. In ortho-toluensulfonamide, where weak attractive interactions occur between the nitrogen lone pair and the methyl hydrogen atoms, the amino group lies in a gauche orientation, retaining the eclipsed configuration with respect to the SO(2) frame. A comparison of the geometrical arrangements found in the PDB database allowed us to understand that the bioactive conformations are different from those found in isolated conditions. The conformations within the receptor are reached with an energy cost, which is balanced by the interactions established in the receptor
Structural characterisation of fenchone and its complexes with ethanol by broadband rotational spectroscopy
Full text linkAlthough significant advances in understanding the human olfactory system have taken place over the last two decades, detailed information on how the interactions between odorants and olfactory receptors occur at the molecular level is still lacking. To achieve a better understanding on the molecular mechanisms involved in olfaction, we are investigating several odorants and their interactions with mimics of amino acid residues in olfactory receptors.
We present here the structural characterisation of fenchone (CHO) and its complexes with ethanol (to mimic the side chain of serine) using a 2-8 GHz chirped-pulse Fourier transform microwave spectrometer built at King’s College London. The rotational spectrum of the parent species and all the C and O isotopologues of fenchone was observed, and from the experimental rotational constants the substitution (r) and effective (r) structures of fenchone were determined. The rotational spectrum of fenchone-ethanol was observed by adding ethanol to the carrier gas and passing the mixture through a receptacle with fenchone. Several 1:1 complexes of fenchone-ethanol have been identified in the rotational spectrum. In all the complexes the ethanol molecule binds to the carbonyl group through an O-H· · · O hydrogen bond.Made available in DSpace on 2017-01-26T21:36:51Z (GMT). No. of bitstreams: 3
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Previous issue date: 2016-06-2
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