1,721,001 research outputs found
Hydrated Complexes of Atmospheric Interest: Rotational Spectrum of Diacetyl-Water
No full textThe rotational spectrum of the molecular complex diacetyl-water has been measured by pulsed jet FTMW spectroscopy. The water molecule acts as an electrofore and induces a dipole moment when combined with non-polar diacetyl. Only one conformer has been observed, corresponding to the global minimum. Its shape is unambiguously established: the water moiety is linked asymmetrically to the organic molecule, it behaves as a proton donor to one of its oxygen atoms and interferes with the internal rotation of the further removed methyl group through a C-HO interaction. Each rotational transition appears as a quintuplet, due to the internal rotation of the two methyl groups, which are non-equivalent in the adduct. From the analysis of the observed splittings, the V3 barriers to the internal rotation of the two methyl groups have been determined to be 3.81(1) and 4.11 (1) kJ/mol, respectively
Morphing the Torsional Potential Energy Function from Local to Global Symmetry through a π Link: The Rotational Spectrum of ALFA, ALFA, ALFA-Trifluoro-p-tolualdehyde
No full textWe report the Fourier transform microwave spectrum of ALFA,ALFA,ALFA-trifluoro-p-tolualdehyde, utilizing internal dynamics to point out spatial orbital effects transferred through a conjugated bond system. The substitution in benzotrifluoride (ALFA,ALFA,ALFA-trifluorotoluene) of the hydrogen atom in position 4 with the aldehyde group breaks the global symmetry of the molecule spatially far away from the 6 locally equivalent minima of the σ-bound CF3 group and dramatically morphs the V6 potential energy function towards a one-order-of-magnitude dominating V3 barrier to the internal rotation of the CF3 top due to the electronic link of the PI-system transmitting the presences of the asymmetry. The value of the determined V3 barrier is 28.862 cm-1
The m = 0 state of the low-barrier torsion in alfa, alfa, alf-trifluorobenzene (benzotrifluoride)
No full textWe observed and assigned the m = 0 spectrum, also for the 13C species in natural abundance, of benzotrifluoride, a molecule with a heavy top undergoing an almost free internal rotation
Proton Transfer in Homodimers of Carboxylic Acids: The Rotational Spectrum of the Dimer of Acrylic Acid
No full textThe dimer of acrylic acid can exist in two forms, depending on the entgegen or zusammen orientations of the two allyl groups. The latter one (zusammen) has a permanent value of the mub dipole moment component, which allowed measuring its pulsed jet Fourier transform microwave (MW) spectrum. From the tunneling splitting, originating in the concerted proton transfer of the two carboxylic hydrogen atoms and measured for four isotopologues of such a bimolecule, we could determine the barrier and dynamics of the proton transfer
Gas-Phase Tautomeric Equilibrium of 4-Hydroxypyrimidine with Its Ketonic Forms: A Free Jet Millimeterwave Spectroscopy Study
No full text4-Hydroxypyrimidine (4HP) has two conformational forms (the hydroxyl hydrogen cis or trans with respect to the adjacent nitrogen), which are in tautomeric equilibrium with two ketonic forms, 4-Pyrimidinone (4PO) and 6-Pyrimidinone (6PO). We have investigated the free jet absorption millimeterwave spectrum of this system, assigning the rotational spectra of 4HPcis and 4PO; the latter species is more stable by 2.0(9) kJ/mol. No lines corresponding to the trans isomer of 4-hydroxypyridine and to 6PO have been observed
Noncovalent Interactions and Internal Dynamics in Dimethoxymethane-Water
No full textThe millimeter-wave absorption and Fourier transform microwave spectra of five isotopologues of the 1:1 adduct dimethoxymethane-water have been measured in supersonic expansions. Each rotational transition appears as a quintuplet, due to the internal rotation of the two methyl groups, which are non-equivalent in the adduct. The water moiety, linked asymmetrically to dimethoxymethane, behaves as a proton donor to one of its oxygen atoms and interferes with the internal rotation of the farther methyl group through a C-HO interaction. From the analysis of the observed splittings, the V3 barriers to the internal rotation of the two methyl groups have been determined to be 6.83(8) and 6.19(8) kJ/mol, respectively. The hydrogen bond structural parameters have been determined, the O-HO and C-HO distances being 1.93(1) and 2.78(4) Å, respectively
Microwave Spectrum of [1,1]-Pyridine-Ne2
No full textWe investigated the rotational spectra of six isotopologues of pyridine-Ne2, formed by the combination of two isotopes of the nitrogen atom (14N and 15N) in pyridine with two isotopes of the rare gas atoms (20Ne and 22Ne), by using pulsed jet Fourier transform microwave spectroscopy. We detected the C2v symmetry conformer denoted as [1,1], where the Ne atoms are located one on each side of the ring plane. The [2,0] species, with the two Ne atoms on the same side of the ring was not observed. Two structural parameters, R and θ, that localize the RG atoms with respect to pyridine, have been determined. The 14N nuclear quadrupole coupling constants have been obtained for the isotopologues containing this nucleus
Rotational Spectrum of Trifluoroacetone
No full textThe rotational spectra of 5 isotopologues of 1,1,1-trifluoroacetone have been assigned using pulsed-jet Fourier-transform microwave spectroscopy. All rotational transitions appear as doublets, due to the internal rotation of the methyl group. Analysis of the tunneling splittings using both the PAM and the CAM methods allows to determine accurately the height of the three-fold barrier to internal rotation of the methyl group, and its orientation, leading to V3 = 3.28 and 3.10 kJmol-1, respectively. The rs geometry of the molecular skeleton, a partial r0 structure of the molecule and supporting ab initio calculations are also reported
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
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