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Articles de revues sur le sujet « Thermochemistry of Molecules and Processes »

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Auteur : Grafiati
Publié le 7 septembre 2023

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1

Pilling, S., G. A. Carvalho, H. A. de Abreu, B. R. L. Galvão, C. H. da Silveira et M. S. Mateus. « Understanding the Molecular Kinetics and Chemical Equilibrium Phase of Frozen CO during Bombardment by Cosmic Rays by Employing the PROCODA Code ». Astrophysical Journal 952, no 1 (1 juillet 2023) : 17. http://dx.doi.org/10.3847/1538-4357/acdb4a.

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Abstract Within the cold regions of space, ices that are enriched with carbon monoxide (CO) molecules are exposed to ionizing radiation, which triggers new reactions and desorption processes. Laboratory studies on astrochemical ices employing different projectiles have revealed the appearance of several new species. In this study, we employed the upgraded PROCODA code, which involves a calculation phase utilizing thermochemistry data, to map the chemical evolution of pure CO ice irradiated by cosmic-ray analogs. In the model, we have considered 18 different chemical species (six observed: CO, CO2, C3, O3, C2O, and C5O3; 12 unobserved: C, O, C2, O2, CO3, C3O, C4O, C5O, C2O2, C2O3, C3O2, and C4O2) coupled at 156 reaction routes. Our best-fit model provides effective reaction rates (effective rate constants, (ERCs)), branching ratios for reactions within reaction groups, several desorption parameters, and the characterization of molecular abundances at the chemical equilibrium (CE) phase. The most abundant species within the ice at the CE phase were atomic oxygen (68.2%) and atomic carbon (18.2%), followed by CO (11.8%) and CO2 (1.6%). The averaged modeled desorption yield and rate were 1.3e5 molecules ion−1 and 7.4e13 molecules s−1, respectively, while the average value of ERCs in the radiation-induced dissociation reactions was 2.4e-1 s−1 and for the bimolecular reactions it was 4.4e-24 cm3 molecule−1 s−1. We believe that the current kinetics study can be used in future astrochemical models to better understand the chemical evolution of embedded species within astrophysical ices under the presence of an ionizing radiation field.
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Marques, Esteban A., Stefan De Gendt, Geoffrey Pourtois et Michiel J. van Setten. « Benchmarking First-Principles Reaction Equilibrium Composition Prediction ». Molecules 28, no 9 (22 avril 2023) : 3649. http://dx.doi.org/10.3390/molecules28093649.

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The availability of thermochemical properties allows for the prediction of the equilibrium compositions of chemical reactions. The accurate prediction of these can be crucial for the design of new chemical synthesis routes. However, for new processes, these data are generally not completely available. A solution is the use of thermochemistry calculated from first-principles methods such as Density Functional Theory (DFT). Before this can be used reliably, it needs to be systematically benchmarked. Although various studies have examined the accuracy of DFT from an energetic point of view, few studies have considered its accuracy in predicting the temperature-dependent equilibrium composition. In this work, we collected 117 molecules for which experimental thermochemical data were available. From these, we constructed 2648 reactions. These experimentally constructed reactions were then benchmarked against DFT for 6 exchange–correlation functionals and 3 quality of basis sets. We show that, in reactions that do not show temperature dependence in the equilibrium composition below 1000 K, over 90% are predicted correctly. Temperature-dependent equilibrium compositions typically demonstrate correct qualitative behavior. Lastly, we show that the errors are equally caused by errors in the vibrational spectrum and the DFT electronic ground state energy.
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Cipriani, Maicol, et Oddur Ingólfsson. « HF Formation through Dissociative Electron Attachment—A Combined Experimental and Theoretical Study on Pentafluorothiophenol and 2-Fluorothiophenol ». International Journal of Molecular Sciences 23, no 5 (23 février 2022) : 2430. http://dx.doi.org/10.3390/ijms23052430.

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In chemoradiation therapy, dissociative electron attachment (DEA) may play an important role with respect to the efficiency of the radiosensitizers used. The rational tailoring of such radiosensitizers to be more susceptive to DEA may thus offer a path to increase their efficiency. Potentially, this may be achieved by tailoring rearrangement reactions into the DEA process such that these may proceed at low incident electron energies, where DEA is most effective. Favorably altering the orbital structure of the respective molecules through substitution is another path that may be taken to promote dissociation up on electron capture. Here we present a combined experimental and theoretical study on DEA in relation to pentafluorothiophenol (PFTP) and 2-fluorothiophenol (2-FTP). We investigate the thermochemistry and dynamics of neutral HF formation through DEA as means to lower the threshold for dissociation up on electron capture to these compounds, and we explore the influence of perfluorination on their orbital structure. Fragment ion yield curves are presented, and the thermochemical thresholds for the respective DEA processes are computed as well as the minimum energy paths for HF formation up on electron capture and the underlying orbital structure of the respective molecular anions. We show that perfluorination of the aromatic ring in these compounds plays an important role in enabling HF formation by further lowering the threshold for this process and through favorable influence on the orbital structure, such that DEA is promoted. We argue that this approach may offer a path for tailoring new and efficient radiosensitizers.
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Hoyermann, Karlheinz, et Johann Seeba. « A direct study of the reaction of benzyl radicals with molecular oxygen : Kinetics and thermochemistry ». Symposium (International) on Combustion 25, no 1 (janvier 1994) : 851–58. http://dx.doi.org/10.1016/s0082-0784(06)80719-8.

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Machado, Hugo G., Flávio O. Sanches-Neto, Nayara D. Coutinho, Kleber C. Mundim, Federico Palazzetti et Valter H. Carvalho-Silva. « “Transitivity” : A Code for Computing Kinetic and Related Parameters in Chemical Transformations and Transport Phenomena ». Molecules 24, no 19 (25 septembre 2019) : 3478. http://dx.doi.org/10.3390/molecules24193478.

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The Transitivity function, defined in terms of the reciprocal of the apparent activation energy, measures the propensity for a reaction to proceed and can provide a tool for implementing phenomenological kinetic models. Applications to systems which deviate from the Arrhenius law at low temperature encouraged the development of a user-friendly graphical interface for estimating the kinetic and thermodynamic parameters of physical and chemical processes. Here, we document the Transitivity code, written in Python, a free open-source code compatible with Windows, Linux and macOS platforms. Procedures are made available to evaluate the phenomenology of the temperature dependence of rate constants for processes from the Arrhenius and Transitivity plots. Reaction rate constants can be calculated by the traditional Transition-State Theory using a set of one-dimensional tunneling corrections (Bell (1935), Bell (1958), Skodje and Truhlar and, in particular, the deformed ( d -TST) approach). To account for the solvent effect on reaction rate constant, implementation is given of the Kramers and of Collins–Kimball formulations. An input file generator is provided to run various molecular dynamics approaches in CPMD code. Examples are worked out and made available for testing. The novelty of this code is its general scope and particular exploit of d -formulations to cope with non-Arrhenius behavior at low temperatures, a topic which is the focus of recent intense investigations. We expect that this code serves as a quick and practical tool for data documentation from electronic structure calculations: It presents a very intuitive graphical interface which we believe to provide an excellent working tool for researchers and as courseware to teach statistical thermodynamics, thermochemistry, kinetics, and related areas.
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RAGHAVACHARI, KRISHNAN, BORIS STEFANOV et LARRY CURTISS. « Accurate density functional thermochemistry for larger molecules ». Molecular Physics 91, no 3 (20 juin 1997) : 555–59. http://dx.doi.org/10.1080/00268979709482745.

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RAGHAVACHARI, By KRISHNAN, BORIS B. STEFANOV et LARRY A. CURTISS. « Accurate density functional thermochemistry for larger molecules ». Molecular Physics 91, no 3 (juin 1997) : 555–60. http://dx.doi.org/10.1080/002689797171445.

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Haworth, Naomi L., Michael B. Sullivan, Angela K. Wilson, Jan M. L. Martin et Leo Radom. « Structures and Thermochemistry of Calcium-Containing Molecules ». Journal of Physical Chemistry A 109, no 40 (octobre 2005) : 9156–68. http://dx.doi.org/10.1021/jp052889h.

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Bouchoux, Guy, Danielle Leblanc, William Bertrand, Terance B. McMahon, Jan E. Szulejko, Florence Berruyer-Penaud, Otilia Mó et Manuel Yáñez. « Protonation Thermochemistry of Selected Hydroxy- and Methoxycarbonyl Molecules ». Journal of Physical Chemistry A 109, no 51 (décembre 2005) : 11851–59. http://dx.doi.org/10.1021/jp054955l.

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Griller, David, J. A. Martinho Simoes, P. Mulder, B. A. Sim et D. D. M. Wayner. « Unifying the solution thermochemistry of molecules, radicals, and ions ». Journal of the American Chemical Society 111, no 20 (septembre 1989) : 7872–76. http://dx.doi.org/10.1021/ja00202a031.

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Bross, David H., et Kirk A. Peterson. « Composite thermochemistry of gas phase U(VI)-containing molecules ». Journal of Chemical Physics 141, no 24 (28 décembre 2014) : 244308. http://dx.doi.org/10.1063/1.4904721.

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Gu, Geun Ho, Petr Plechac et Dionisios G. Vlachos. « Thermochemistry of gas-phase and surface species via LASSO-assisted subgraph selection ». Reaction Chemistry & ; Engineering 3, no 4 (2018) : 454–66. http://dx.doi.org/10.1039/c7re00210f.

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13

Nagy, Balázs, Péter Szakács, József Csontos, Zoltán Rolik, Gyula Tasi et Mihály Kállay. « High-Accuracy Theoretical Thermochemistry of Atmospherically Important Sulfur-Containing Molecules ». Journal of Physical Chemistry A 115, no 26 (7 juillet 2011) : 7823–33. http://dx.doi.org/10.1021/jp203406d.

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Barreto, Patr�cia R. P., Alessandra F. A. Vilela et Ricardo Gargano. « Thermochemistry of molecules in the B/F/H/N system ». International Journal of Quantum Chemistry 103, no 5 (2005) : 659–84. http://dx.doi.org/10.1002/qua.20566.

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Karton, Amir. « A computational chemist's guide to accurate thermochemistry for organic molecules ». Wiley Interdisciplinary Reviews : Computational Molecular Science 6, no 3 (15 février 2016) : 292–310. http://dx.doi.org/10.1002/wcms.1249.

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Roux, María Victoria, Concepción Foces-Foces et Rafael Notario. « Thermochemistry of organic molecules : The way to understand energy–structure relationships ». Pure and Applied Chemistry 81, no 10 (3 octobre 2009) : 1857–70. http://dx.doi.org/10.1351/pac-con-08-10-01.

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The combination of experimental calorimetric measurements, particularly of the standard energies and enthalpies of combustion and formation, and theoretical examination of model molecules constitutes a powerful tool for the understanding of the conformational and chemical behavior of organic molecules. In this article, several examples are provided where the synergy between experiment and theory made possible the comprehension of various fundamental interactions in oxygen- and sulfur-containing six-membered heterocyclic compounds, the determination of the strain energy in two C8H8 derivatives, dimethyl cubane-1,4-dicarboxylate and dimethyl cuneane-2,6-dicarboxylate, and the calculation of the enthalpies of formation of the parent compounds, cubane and cuneane, and the study of the energy–structure relationship in barbituric acid.
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17

Zachariah, Michael R., et Carl F. Melius. « Theoretical Calculation of Thermochemistry for Molecules in the Si−P−H System ». Journal of Physical Chemistry A 101, no 5 (janvier 1997) : 913–18. http://dx.doi.org/10.1021/jp9617377.

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Ramabhadran, Raghunath O., et Krishnan Raghavachari. « Theoretical Thermochemistry for Organic Molecules : Development of the Generalized Connectivity-Based Hierarchy ». Journal of Chemical Theory and Computation 7, no 7 (24 juin 2011) : 2094–103. http://dx.doi.org/10.1021/ct200279q.

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19

Raghavachari, Krishnan, Boris B. Stefanov et Larry A. Curtiss. « Accurate thermochemistry for larger molecules : Gaussian-2 theory with bond separation energies ». Journal of Chemical Physics 106, no 16 (22 avril 1997) : 6764–67. http://dx.doi.org/10.1063/1.473659.

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Nagy, Balázs, Péter Szakács, József Csontos, Zoltán Rolik, Gyula Tasi et Mihály Kállay. « Correction to “High-Accuracy Theoretical Thermochemistry of Atmospherically Important Sulfur-Containing Molecules” ». Journal of Physical Chemistry A 117, no 24 (7 juin 2013) : 5220. http://dx.doi.org/10.1021/jp405361p.

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21

Ishikawa, Atsushi, Masahiro Kamata et Hiromi Nakai. « Quantum chemical approach for condensed-phase thermochemistry (IV) : Solubility of gaseous molecules ». Chemical Physics Letters 655-656 (juillet 2016) : 103–9. http://dx.doi.org/10.1016/j.cplett.2016.05.041.

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22

Allendorf, Mark D., et Carl F. Melius. « Theoretical study of thermochemistry of molecules in the silicon-carbon-chlorine-hydrogn system ». Journal of Physical Chemistry 97, no 3 (janvier 1993) : 720–28. http://dx.doi.org/10.1021/j100105a031.

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Allendorf, Mark D., et Carl F. Melius. « Theoretical study of the thermochemistry of molecules in the silicon-carbon-hydrogen system ». Journal of Physical Chemistry 96, no 1 (janvier 1992) : 428–37. http://dx.doi.org/10.1021/j100180a080.

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24

Allendorf, Mark D., Carl F. Melius, Pauline Ho et Michael R. Zachariah. « Theoretical Study of the Thermochemistry of Molecules in the Si-O-H System ». Journal of Physical Chemistry 99, no 41 (octobre 1995) : 15285–93. http://dx.doi.org/10.1021/j100041a052.

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Pople, John A., Brian T. Luke, Michael J. Frisch et J. Stephen Binkley. « Theoretical thermochemistry. 1. Heats of formation of neutral AHn molecules (A = Li to Cl) ». Journal of Physical Chemistry 89, no 11 (mai 1985) : 2198–203. http://dx.doi.org/10.1021/j100257a013.

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Ho, Pauline, et Carl F. Melius. « Theoretical Study of the Thermochemistry of Molecules in the Si-O-H-C System ». Journal of Physical Chemistry 99, no 7 (février 1995) : 2166–76. http://dx.doi.org/10.1021/j100007a056.

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Melius, Carl F., et Pauline Ho. « Theoretical study of the thermochemistry of molecules in the silicon-nitrogen-hydrogen-fluorine system ». Journal of Physical Chemistry 95, no 3 (février 1991) : 1410–19. http://dx.doi.org/10.1021/j100156a070.

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Ho, Pauline, Michael E. Colvin et Carl F. Melius. « Theoretical Study of the Thermochemistry of Molecules in the Si−B−H−Cl System ». Journal of Physical Chemistry A 101, no 49 (décembre 1997) : 9470–88. http://dx.doi.org/10.1021/jp971947z.

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Martin, Jan M. L., Peter R. Taylor, J. P. François et R. Gijbels. « Ab initio study of the spectroscopy and thermochemistry of the C2N and CN2 molecules ». Chemical Physics Letters 226, no 5-6 (août 1994) : 475–83. http://dx.doi.org/10.1016/0009-2614(94)00758-6.

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Gheorghe, Daniela, Ana Neacsu et Stefan Perisanu. « Thermochemistry of Eight Membered Ring Hydrocarbons. The Enthalpy of Formation of Cyclooctane ». Revista de Chimie 71, no 3 (1 janvier 2001) : 507–15. http://dx.doi.org/10.37358/rc.20.3.8025.

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A new value of the enthalpy of formation of cyclooctane (-156.2�1.2 kJ mol-1) based on heat of combustion measurements is reported. Its solid - liquid phase change was investigated by differential scanning calorimetry in both directions revealing an overcooling effect of over 23 K. Our enthalpy of formation of cyclooctane was used together with literature values of heats of hydrogenation of 8 carbon atoms cycloolefins to calculate the enthalpies of formation of the later. The strain energies of the investigated molecules were calculated and discussed.
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31

Harvey, Jean-Philippe, Francis Lebreux-Desilets, Jeanne Marchand, Kentaro Oishi, Anya-Fettouma Bouarab, Christian Robelin, Aimen E. Gheribi et Arthur D. Pelton. « On the Application of the FactSage Thermochemical Software and Databases in Materials Science and Pyrometallurgy ». Processes 8, no 9 (15 septembre 2020) : 1156. http://dx.doi.org/10.3390/pr8091156.

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The discovery of new metallic materials is of prime importance for the development of new technologies in many fields such as electronics, aerial and ground transportation as well as construction. These materials require metals which are obtained from various pyrometallurgical processes. Moreover, these materials need to be synthesized under extreme conditions of temperature where liquid solutions are produced and need to be contained. The design and optimization of all these pyrometallurgical processes is a key factor in this development. We present several examples in which computational thermochemistry is used to simulate complex pyrometallurgical processes including the Hall–Heroult process (Al production), the PTVI process (Ni production), and the steel deoxidation from an overall mass balance and energy balance perspective. We also show how computational thermochemistry can assist in the material selection in these extreme operation conditions to select refractory materials in contact with metallic melts. The FactSage thermochemical software and its specialized databases are used to perform these simulations which are proven here to match available data found in the literature.
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32

GOLOVIN, A. V., D. A. PONOMAREV et V. V. TAKHISTOV. « THERMOCHEMISTRY OF ORGANIC, HETEROORGANIC, AND INORGANIC MOLECULES AND THEIR FRAGMENTS : "QUANTUM-CHEMICAL CALCULATIONS OF THERMOCHEMICAL PARAMETERS : MOLECULES AND THEIR FRAGMENTS" ». Journal of Theoretical and Computational Chemistry 09, supp01 (janvier 2010) : 125–53. http://dx.doi.org/10.1142/s0219633610005529.

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Analysis of theoretical enthalpies of formation for about 300 molecules and their fragments (free radicals, biradicals, and ions) was performed to show that the results of semiempirical, DFT, and ab initio methods must be taken with great caution. A brief review of the authors' alternative empirical methodologies for calculation of enthalpies of formation for molecules (enthalpic shift procedure) and free radicals (enthalpies of isodesmic reactions) is given.
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Bogdan, Diana, et Valer Tosa. « Processes in Isotopes and Molecules ». Journal of Physics : Conference Series 182 (1 juillet 2009) : 011001. http://dx.doi.org/10.1088/1742-6596/182/1/011001.

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34

van Dishoeck, Ewine F. « Photodissociation Processes of Astrophysical Molecules ». Symposium - International Astronomical Union 120 (1987) : 51–65. http://dx.doi.org/10.1017/s0074180900153793.

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35

Letokhov, V. S. « Infrared multiphoton processes in molecules ». Applied Physics B Photophysics and Laser Chemistry 47, no 3 (novembre 1988) : 207. http://dx.doi.org/10.1007/bf00697338.

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Navrotsky, Alexandra. « Thermochemistry of New, Technologically Important Inorganic Materials ». MRS Bulletin 22, no 5 (mai 1997) : 35–41. http://dx.doi.org/10.1557/s0883769400033182.

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The past decade has seen exciting advances in the discovery, improved synthesis and processing, and molecular level engineering of new inorganic materials having specialized electronic, ceramic, and structural applications. Many such materials share two common characteristics: They are complex in structure and composition (think for example of oxide superconductors), and they must be prepared by a series of steps under carefully controlled conditions (consider the intricacies of zeolite synthesis for example). The use of low-temperature aqueous synthesis conditions, with appropriate attention to pH, inorganic and organic structure-directing agents, and subsequent drying and calcination protocols has led to a wealth of new and often metastable crystalline polymorphs, to amorphous materials, and to fine powders with particles of nanoscale dimensions. Methods such as sol-gel synthesis, chimie douce (soft chemistry), hydrothermal synthesis, chemical vapor deposition, and various beam-deposition and epitaxy techniques produce a wealth of materials not constrained to be in chemical equilibrium with their surroundings and not representing the state of lowest free energy. Modern materials chemists almost have their pet Maxwell Demon to select atoms at will and cause them to assemble in a structure of controllable dimensions. The wealth of possible new structures formed begins to mimic the riches of organic chemistry. In this field, the fact that all complex organic and biochemical molecules are metastable under ambient conditions with respect to a mixture of carbon dioxide, water, and other simple gases is irrelevant except in a conflagration.Liberation of ceramic science from the tyranny of high-temperature equilibrium is thus leading to new materials synthesized more quickly, at lower cost, and under environmentally more friendly conditions. There is of course a price to pay. First the synthetic procedures are more complex than traditional “mix, grind, fire, and repeat” ceramic processing. Second and more importantly, very little is known about the long-term stability of the materials formed, about their degradation during use, and about materials compatibility. Two examples of such problems are the potential corrosion of high Tc YBCO superconductors by ambient H2O and CO2, and the collapse to inactive phases of complex zeolitic and mesoporous catalysts under operating conditions. Chemical reactions in metastable materials are governed by an intertwined combination of thermodynamic driving forces and kinetic rates. For this rich landscape of new materials, neither the depths of the valleys nor the heights of the mountains are known. Often one cannot even tell which way is energetically downhill.
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Ottonello, G., et M. Vetuschi Zuccolini. « Ab initio thermochemistry of some geochemically relevant molecules in the system Cr-O-H-Cl ». Geochimica et Cosmochimica Acta 69, no 14 (juillet 2005) : 3505–18. http://dx.doi.org/10.1016/j.gca.2005.02.012.

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38

Lago, A. F., et Tomas Baer. « Dissociation dynamics and thermochemistry of chloroform and tetrachloroethane molecules studied by threshold photoelectron photoion coincidence ». International Journal of Mass Spectrometry 252, no 1 (mai 2006) : 20–25. http://dx.doi.org/10.1016/j.ijms.2006.01.013.

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Harkins, Robin P., Christopher J. Cramer et Wayne L. Gladfelter. « Computational Thermochemistry of Mono- and Dinuclear Tin Alkyls Used in Vapor Deposition Processes ». Journal of Physical Chemistry A 123, no 7 (12 février 2019) : 1451–60. http://dx.doi.org/10.1021/acs.jpca.8b12072.

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40

Izato, Yu-ichiro, Akira Matsugi, Mitsuo Koshi et Atsumi Miyake. « A simple heuristic approach to estimate the thermochemistry of condensed-phase molecules based on the polarizable continuum model ». Physical Chemistry Chemical Physics 21, no 35 (2019) : 18920–29. http://dx.doi.org/10.1039/c9cp03226f.

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41

HEINE, BARBARA. « Fast transfer processes in organic molecules† ». International Journal of Electronics 70, no 3 (mars 1991) : 505–8. http://dx.doi.org/10.1080/00207219108921301.

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42

BOHR, HENRIK, PER GREISEN et BARRY MALIC. « EXCITED STATE PROCESSES IN PHOTOSYNTHESIS MOLECULES ». International Journal of Modern Physics B 22, no 25n26 (20 octobre 2008) : 4617–26. http://dx.doi.org/10.1142/s0217979208050371.

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A study of electronic processes in the chlorophyll and carothenoid molecules of the photo-reaction center II is presented with the focus on the electronic excitations and charge transfer in the photosynthetic process. Several novel ideas are mentioned especially concerning the electron replenishment and nuclear vibrational excitations. The study is build mainly on numerical quantum calculations of electronic structures of molecules in the photo-reaction center.
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43

Hill, S. M., P. J. Milla, T. Caseseca et R. Mirakian. « Cell adhesion molecules in enteropathic processes ». Pediatric Research 27, no 5 (mai 1990) : 531. http://dx.doi.org/10.1203/00006450-199005000-00033.

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44

Sieck, L. Wayne. « Thermochemistry of solvation of sulfur hexafluoride monoanion by simple polar organic molecules in the vapor phase ». Journal of Physical Chemistry 90, no 25 (décembre 1986) : 6684–87. http://dx.doi.org/10.1021/j100283a018.

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Gong, Liangfa, Qianshu Li, Wenguo Xu, Yaoming Xie et Henry F. Schaefer. « Novel Interhalogen Molecules : Structures, Thermochemistry, and Electron Affinities of Dibromine Fluorides Br2Fn/Br2Fn-(n= 1−6) ». Journal of Physical Chemistry A 108, no 16 (avril 2004) : 3598–614. http://dx.doi.org/10.1021/jp031311+.

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HO, P., M. E. COLVIN et C. F. MELIUS. « ChemInform Abstract : Theoretical Study of the Thermochemistry of Molecules in the Si-B-H-Cl System. » ChemInform 29, no 12 (23 juin 2010) : no. http://dx.doi.org/10.1002/chin.199812011.

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Holmes, John L., Karl J. Jobst et Johan K. Terlouw. « Small (Poly)Unsaturated Oxygen Containing Ions and Molecules : A Brief Assessment of Their Thermochemistry Based on Computational Chemistry ». European Journal of Mass Spectrometry 15, no 2 (avril 2009) : 261–73. http://dx.doi.org/10.1255/ejms.959.

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The CBS-QB3, CBS-APNO and Gaussian-3 model chemistries have been used to determine the ionic and neutral heats of formation and the adiabatic ionization energies ( IEa) derived therefrom, for the ca 30 principal isomers of the C3H2O•+ and the C4H4O•+ families of radical cations. Theory and experiment are in excellent agreement for those molecules whose experimental IEa has been accurately measured. In contrast, large deviations from the computed values were found for a great many ionic heats of formation reported in the literature. These deviations largely arise from the uncertainty in the heat of formation of the corresponding neutral species for which often only a rough estimate is available. A useful by-product of this study is that it permits the evaluation of new Benson-type group additivity ( GA) terms appropriate for highly unsaturated oxygen containing molecules. Several new GA terms are proposed but it is also argued that a single GA term for the ketene function cannot be defined.
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Poon, Clement, et Paul M. Mayer. « Electron-spin conservation and methyl-substitution effects on bonds in closed- and open-shell systems — A G3 ab initio study of small boron-containing molecules and radicals ». Canadian Journal of Chemistry 80, no 1 (1 janvier 2002) : 25–30. http://dx.doi.org/10.1139/v01-185.

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High level ab initio molecular orbital theory calculations have been used to study the geometries and thermochemistry of molecules and free radicals substituted by BH2, BHCH3, and B(CH3)2. The heats of formation and RR'B—X bond strengths (RR' = H, H; H, CH3; CH3, CH3 and X = CH3, NH2, OH, F, SiH3, PH2, SH, and Cl) together with those for the open-shell systems RR'B—Y· (RR' = H, H; H, CH3; CH3, CH3 and Y = CH2, NH, O, SiH2, PH, and S) have been calculated at the G3 level of theory. The trends observed for the homolytic bond strengths in the closed-shell systems are those expected from electronegativity arguments, i.e., as the difference in electronegativity between the two atoms in the B—X bond increases, the bond strength increases. Methyl substitution on B in the closed- and open-shell species increases the ionic contribution to the bond thereby decreasing the bond strength. The lowest possible homolytic dissociation energy for the free radicals RR'BY· is lower than those of their closed-shell counterparts, yet the B—Y· bonds are shorter. This is due to the demands of spin conservation in the dissociation of the radicals favouring the formation of higher energy products.Key words: ab initio calculations, bond dissociation energy, organoboron compounds, thermochemistry.
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Abdel-Halim, Hamzeh M., et Sawsan M. Jaafreh. « Reaction Rate Constants from Classical Trajectories of Atom-Diatomic Molecule Collisions ». Zeitschrift für Naturforschung A 63, no 3-4 (1 avril 2008) : 159–69. http://dx.doi.org/10.1515/zna-2008-3-408.

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Classical trajectory calculations for various atom-diatomic molecules were preformed using the three-dimensional Monte Carlo method. The reaction probabilities, cross-sections and rate constants of several systems were calculated. Equations of motion, which predict the positions and momenta of the colliding particles after each step, have been integrated numerically by the Runge-Kutta-Gill and Adams-Moulton methods. Morse potential energy surfaces were used to describe the interaction between the atom and each atom in the diatomic molecules. The results were compared with experimental ones and with other theoretical values. Good agreement was obtained between calculated rate constants and those obtained experimentally. Also, reasonable agreement was observed with theoretical rate constants obtained by other investigators using different calculation methods. The effects of the temperature, the nature of the colliding particles and the thermochemistry were studied. The results showed a strong dependence of the reaction rates on these factors.
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Simonnet, M., J. F. Domgin, J. Lehmann et P. Gardin. « Numerical Tool Coupling Fluid Dynamics and Thermochemistry to Predict and to Optimize Deoxidation Processes ». BHM Berg- und Hüttenmännische Monatshefte 152, no 11 (novembre 2007) : 350–54. http://dx.doi.org/10.1007/s00501-007-0327-4.

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