166,051 research outputs found
Falloff curves and mechanism of thermal decomposition of CF3I in shock waves
No full textThe falloff curves of the unimolecular dissociation CF3I (+Ar) - CF3 + I (+Ar) are modelled by combining quantum-chemical characterizations of the potential energy surface for the reaction, standard unimolecular rate theory, and experimental information on the average energy transferred per collision between excited CF3I and Ar. The (essentially) parameter-free theoretical modelling gives results in satisfactory agreement with data deduced from earlier shock wave experiments employing a variety of reactant concentrations (between a few ppm and a few percent in the bath gas Ar). New experiments recording absorption–time signals of CF3I, I2, CF2 and (possibly) IF at 450–500 and 200–300 nm are reported. By analysing the decomposition mechanism, besides the unimolecular dissociation of CF3I, these provide insight into the influence of secondary reactions on the experimental observations.Fil: Cobos, Carlos Jorge. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; ArgentinaFil: Sölter, L.. Universität Göttingen; AlemaniaFil: Tellbach, E.. Universität Göttingen; AlemaniaFil: Troe, J.. Universität Göttingen; Alemania. Institut Max Planck fuer Bioanorganische Chemie; Alemani
Shock wave and modeling study of the thermal decomposition reactions of Pentafluoroethane and 2-H Heptafluoropropane
No full textThe thermal decomposition reactions of CF3CF2H and CF3CFHCF3 have been studied in shock waves by monitoring the appearance of CF2 radicals. Temperatures in the range 1400-2000 K and Ar bath gas concentrations in the range (2-10) × 10(-5) mol cm(-3) were employed. It is shown that the reactions are initiated by C-C bond fission and not by HF elimination. Differing conclusions in the literature about the primary decomposition products, such as deduced from experiments at very low pressures, are attributed to unimolecular falloff effects. By increasing the initial reactant concentrations in Ar from 60 to 1000 ppm, a retardation of CF2 formation was observed while the final CF2 yields remained close to two CF2 per C2F5H or three CF2 per C3F7H decomposed. This is explained by secondary bimolecular reactions which lead to comparably stable transient species like CF3H, releasing CF2 at a slower rate. Quantum-chemical calculations and kinetic modeling help to identify the reaction pathways and provide estimates of rate constants for a series of primary and secondary reactions in the decomposition mechanism.Fil: Cobos, Carlos Jorge. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico la Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; Argentina. Universidad Nacional de La Plata; ArgentinaFil: Sölter, L.. Universitat of Gottingen; AlemaniaFil: Tellbach, E.. Universitat of Gottingen; AlemaniaFil: Troe, J.. Max-Planck-Institut für Biophysikalische Chemie; Alemani
Shock Wave Study of the Thermal Dissociations of C3F6 and c-C3F6. I. Dissociation of Hexafluoropropene
No full textThe thermal dissociation of C3F6 was studied between 1330 and 2210 K in shock waves monitoring the UV absorption of CF2. CF2 yields of about 2.6 per parent C3F6 were obtained at reactant concentrations of 500-1000 ppm in the bath gas Ar. These yields dropped to about 1.8 when reactant concentrations were lowered to 60 ppm. The increase of the CF2 yield with increasing concentration was attributed to bimolecular reactions between primary and secondary dissociation products. Quantum-chemical and kinetic modeling calculations helped to estimate the contributions from the various primary dissociation steps. It was shown that the measurements correspond to unimolecular reactions in their falloff range. Falloff representations of the rate constants are given, leading to an overall high pressure rate constant k∞ = 2.0 × 10(17)(-104 kcal mol(-1)/RT) s(-1) and a relative rate of about 2/3:1/3 for the reactions C3F6 → CF3CF + CF2 versus C3F6 → C2F3 + CF3.Fil: Cobos, Carlos Jorge. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico la Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; Argentina. Universidad Nacional de La Plata; ArgentinaFil: Sölter, L.. Universitat of Gottingen; AlemaniaFil: Tellbach, E.. Universitat of Gottingen; AlemaniaFil: Troe, J.. Max-Planck-Institut für Biophysikalische Chemie; Alemania. Universitat of Gottingen; Alemani
M. J. Tricart, Quelques caractéristiques générales des villes latino-américaines
No full textPradilla Cobos Emilio. M. J. Tricart, Quelques caractéristiques générales des villes latino-américaines. In: Tiers-Monde, tome 8, n°32, 1967. L'Espagne à l'heure du développement. pp. 1203-1204
Prediction of reduced falloff curves for recombination reactions at low temperatures
No full textStrong collision falloff curves for barrierless recombination reactions at low temperatures are calculated taking into account transitional modes only. Specific rate constants k(E, J) from statistical adiabatic channel/classical trajectory (SACM/CT) calculations are used. Broadening factors of the falloff curves are found to depend only weakly on the temperature. A systematic analysis of the influence of the centrifugal barriers E-0(J), which are governed by the potential energy surface of the bond energies E-0, and of the number of transitional modes is made. Guidelines for estimating center broadening factors and shape functions for the broadening factors are given
The Thermal DissociationRecombination Reactions of SiF4, SiF3, and SiF2: A Shock Wave and Theoretical Modeling Study
No full textMonitoring UV absorption signals of SiF2and SiF, the thermal dissociation reactions of SiF4and SiF2were studied in shock waves. Rationalizing the experimental observations by standard unimolecular rate theory in combination with quantum-chemical calculations of the reaction potentials, rate constants for the thermal dissociation reactions of SiF4, SiF3, and SiF2and their reverse recombination reactions were determined over broad temperature and pressure ranges. A comparison of fluorosilicon and fluorocarbon chemistry was finally made.Fil: Cobos, Carlos Jorge. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; ArgentinaFil: Sölter, Lars. Universität Göttingen; Alemania. Max-Planck-Institut für Multidisziplinäre Naturwissenschaften; AlemaniaFil: Tellbach, Elsa. Universität Göttingen; Alemania. Max-Planck-Institut für Multidisziplinäre Naturwissenschaften; AlemaniaFil: Troe, Jürgen. Universität Göttingen; Alemania. Max-Planck-Institut für Multidisziplinäre Naturwissenschaften; Alemani
Shock wave studies of the pyrolysis of fluorocarbon oxygenates. II. the thermal dissociation of C4F8O
No full textThe thermal decomposition of octafluorooxalane, C4F8O, to C2F4 + CF2 + COF2 has been studied in shock waves highly diluted in Ar between 1300 and 2200 K. The primary dissociation was shown to be followed by secondary dissociation of C2F4 and dimerization of CF2. The primary dissociation was found to be in its falloff range and falloff curves were constructed. The limiting low and high pressure rate constants were estimated and compared with modelling results. Quantum-chemical calculations identified possible reaction pathways, either leading directly to the final products of the reaction or passing through an open-chain CF2CF2CF2 intermediate which dissociates in a second step.Fil: Cobos, Carlos Jorge. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; ArgentinaFil: Hintzer, K.. Dyneon GmbH; AlemaniaFil: Sölter, L.. Universität Göttingen; AlemaniaFil: Tellbach, E.. Universität Göttingen; AlemaniaFil: Thaler, A.. Dyneon GmbH; AlemaniaFil: Troe, J.. Universität Göttingen; Alemania. Max-Planck-Institut für Biophysikalische Chemie; Alemani
Oblitosaurus Sánchez-Fenollosa & Verdú & Cobos 2023, gen.nov.
No full text<i>Oblitosaurus</i> gen.nov. <p> <i>Etymology:</i> The generic name <i>Oblitosaurus</i> from ‘oblitus’ (Latin), meaning forgoưen, because its bones are the last to be studied from the Barrihonda-El Humero fossil site. And from ‘sauros’ (Greek), meaning lizard.</p> <p> <i>Type species: Oblitosaurus bunnueli</i> gen. et sp. nov.</p> <p> <i>Diagnosis:</i> As for type and only species (see below).</p>Published as part of <i>Sánchez-Fenollosa, Sergio, Verdú, Francisco J. & Cobos, Alberto, 2023, The largest ornithopod (Dinosauria: Ornithischia) from the Upper Jurassic of Europe sheds light on the evolutionary history of basal ankylopollexians, pp. 1013-1033 in Zoological Journal of the Linnean Society 199 (4)</i> on page 1015, DOI: 10.1093/zoolinnean/zlad076, <a href="http://zenodo.org/record/10470514">http://zenodo.org/record/10470514</a>
Agrilaxia (Agrilaxia) simillima Cobos 1972
No full textAgrilaxia (Agrilaxia) simillima (Cobos, 1972) (Fig. 4) Anthaxia (Agrilaxia) simillima Cobos, 1972: 109. Anthaxia (Agrilaxia) simillima: Bílý, 1997: 36, 115 (catalogue). Agrilaxia simillima: Bellamy, 2008: 1507 (catalogue). Type specimen studied. Holotype by monotypy (male, NHMB): “ 2176 [blue, h] // Costa Rica Schmidt S. [p, framed] // cum typo comp. Dr. Hoscheck [p, framed] // Museum Frey Tutzing [green, p] // schmidti Obb. sec. Hoscheck [h, Cobos] // Holotypus [p, red]// Anthaxia (Agrilaxia) simillima nov. sp. Holotypus [h] A. Cobos det. 1968 [p]” Further specimens studied. COSTA RICA: Puntarenas, Manuel Antonio, 20.iii. 1996, Dr. D. Dauber leg. (1 male, NMPC); VENEZUELA: Aragua, Rancho Grande, 700 m, 14.ix. 1970, J. & B. Bechyně leg. (1 male—Fig. 4, MIZA); Barinas, Soledad, Carretera I, 1100 m, 22.viii. 1974, B. Bechyně leg. (1 male, NMPC). Note. This species was described for a single male from Costa Rica in the genus Anthaxia (Cobos, 1972); the female is unknown. Distribution. Costa Rica, Venezuela (new country record).Published as part of Bílý, Svatopluk, 2015, A study on the genus Agrilaxia Kerremans, 1903 from Venezuela (Coleoptera: Buprestidae: Buprestinae: Anthaxiini), pp. 173-182 in Zootaxa 4039 (1) on page 175, DOI: 10.11646/zootaxa.4039.1.8, http://zenodo.org/record/23984
Shock wave studies of the pyrolysis of fluorocarbon oxygenates. I. The thermal dissociation of C3F6O and CF3COF
No full textThe thermal decomposition of hexafluoropropylene oxide, C3F6O, to perfluoroacetyl fluoride, CF3COF, and CF2 has been studied in shock waves highly diluted in Ar between 630 and 1000 K. The measured rate constant k1 = 1.1 × 1014exp(-162(±4) kJ mol-1/RT) s-1 agrees well with literature data and modelling results. Using the reaction as a precursor, equimolar mixtures of CF3COF and CF2 were further heated. Combining experimental observations with theoretical modelling (on the CBS-QB3 and G4MP2 ab initio composite levels), CF3COF is shown to dissociate on two channels, either leading to CF2 + COF2 or to CF3 + FCO. By monitoring the CF2 signals, the branching ratio was determined between 1400 and 1900 K. The high pressure rate constants for the two channels were obtained from theoretical modelling as k5,∞(CF3COF → CF2 + COF2) = 7.1 × 1014exp(-320 kJ mol-1/RT) s-1 and k6,∞(CF3COF → CF3 + FCO) = 3.9 × 1015exp(-355 kJ mol-1/RT) s-1. The experimental results obtained at [Ar] ≈ 5 × 10-6 mol cm-3 were consistent with modelling results, showing that the reaction is in the falloff range of the unimolecular dissociation. The mechanism of secondary reactions following CF3COF dissociation has been analysed as well.Fil: Cobos, Carlos Jorge. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; ArgentinaFil: Hintzer, K.. Dyneon GmbH; AlemaniaFil: Sölter, L.. Universität Göttingen; AlemaniaFil: Tellbach, E.. Universität Göttingen; AlemaniaFil: Thaler, A.. Dyneon GmbH; AlemaniaFil: Troe, J.. Universität Göttingen; Alemania. Max-Planck-Institut für Biophysikalische Chemie; Alemani
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