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Constant Calculations (constant + calculation)

Distribution by Scientific Domains
Chemistry66%

Selected Abstracts

Theoretical study and rate constant calculation for reaction of CF3CH2OH with OH

JOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 4 2007
Ying Wang
Abstract The reaction mechanism of CF3CH2OH with OH is investigated theoretically and the rate constants are calculated by direct dynamics method. The potential energy surface (PES) information, which is necessary for dynamics calculation, is obtained at the B3LYP/6-311G (d, p) level. The single-point energy calculations are performed at the MC-QCISD level using the B3LYP geometries. Complexes, with the energies being less than corresponding reactants and products, are found at the entrance and exit channels for methylene-H-abstraction channel, while for the hydroxyl-H-abstraction channel only entrance complex is located. By means of isodesmic reactions, the enthalpies of the formation for the species CF3CH2OH, CF3CHOH, and CF3CH2O are estimated at the MC-QCISD//B3LYP/6-311G (d, p) level of theory. The rate constants for two kinds of H-abstraction channels are evaluated by canonical variational transition state theory with the small-curvature tunneling correction (CVT/SCT) over a wide range of temperature 200,2000 K. The calculated results are in good agreement with the experimental values in the temperature region 250,430 K. The present results indicate that the two channels are competitive. Below 289 K, hydroxyl-H-abstraction channel has more contribution to the total rate constants than methylene-H-abstraction channel, while above 289 K, methylene-H-abstraction channel becomes more important and then becomes the major reaction channel. © 2007 Wiley Periodicals, Inc. J Comput Chem 28: 802,810, 2007 [source]

Force constant calculation from Raman and IR spectra in the three non-cubic phases of BaCeO3

JOURNAL OF RAMAN SPECTROSCOPY, Issue 5 2001
H. C. Gupta
Raman spectroscopic data for BaCeO3 were modeled with the use of a small set of force constants in its three phases (Pnma, Imma and R3c) using experimental IR and Raman data. An IR reflectance spectrum of BaCeO3 in its Pnma phase is provided for the first time. Raman band symmetry assignments in the Pnma phase were re-examined and the assignments of Genet et al. were confirmed. The distribution of the Raman bands of the Pnma phase between the zone center and X point in Imma is provided and band assignments were extended to the Imma and R3c phases. Calculated values for both Raman- and IR-active modes are provided in the three phases. The variations in force constants throughout the phase transitions are briefly discussed. Copyright © 2001 John Wiley & Sons, Ltd. [source]

A MATLAB toolbox for solving acid-base chemistry problems in environmental engineering applications

COMPUTER APPLICATIONS IN ENGINEERING EDUCATION, Issue 4 2005
Chetan T. Goudar
Abstract A MATLAB toolbox incorporating several computer programs has been developed in an attempt to automate laborious calculations in acid-base chemistry. Such calculations are routinely used in several environmental engineering applications including the design of wastewater treatment systems and for predicting contaminant fate and transport in the subsurface. The computer programs presented in this study do not replace student thinking involved in formulating the problem solving strategy but are merely tools that simplify the actual problem solving process. They encompass a wide variety of acid-base chemistry topics including equilibrium constant calculations, construction of distribution diagrams for mono and multiprotic systems, ionic strength and activity coefficient calculations, and buffer index calculations. All programs are characterized by an intuitive graphical user interface where the user supplies input information. Program outputs are either numerical or graphical depending upon the nature of the problem. The application of this approach to solving actual acid-base chemistry problems is illustrated by computing the pH and equilibrium composition of a 0.1 M Na2CO3 system at 30°C using several programs in the toolbox. As these programs simplify lengthy computations such as ionization fraction and activity coefficient calculations, it is hoped they will help bring more complicated problems to the environmental engineering classroom and enhance student understanding of important concepts that are applicable to real-world systems. The programs are available free of charge for academic use from the authors. © 2005 Wiley Periodicals, Inc. Comput Appl Eng Educ 13: 257,265, 2005; Published online in Wiley InterScience (www.interscience.wiley.com); DOI 10.1002/cae.20051 [source]

Kinetics and mechanism for the H-for-X exchange process in the H + C6H5X reactions: A computational study

INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 11 2001
I. V. Tokmakov
The addition of H atoms to benzene and toluene and subsequent transformations were investigated using high level ab initio and density functional theory methods. Molecular structures and vibrational frequencies calculated at the B3LYP/6-311++G(d,p) level of theory were used in combination with adjusted G2M energetic parameters for RRKM rate constant calculations. Standard heats of formation for cyclohexadienyl and cyclohexadienyl, 6-methyl radicals calculated through isodesmic reactions amounted to 49.5 ± 2 and 42.9 ± 3 kcal/mol, respectively. Rate constants for various elementary reactions involved in the H-for-X exchange (X = D, CH3) were calculated and closely correlated with the available experimental kinetic data. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 633,653, 2001 [source]

Magnetic and electronic properties of transition metal nitride strained layers

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 2 2007
M. Ribeiro Jr.
Abstract We present a theoretical study with ab initio techniques on magnetic and electronic properties of 3d transition metal mononitrides. We perform the calculations in the wurtzite (w) and the zincblende (zb) structures, and find the tendency of all zb mononitrides to become half-metallic (HM) under hydrostatic strain. MnN, CrN, and VN become HM with integer magnetic moments of 4, 3 and 2,B, respectively. CrN shows ferromagnetism (FM) throughout the range of our lattice constant calculations, while VN is FM beyond the lattice constant of 4.65 Ĺ. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Theoretical and experimental NMR study of protopine hydrochloride isomers

MAGNETIC RESONANCE IN CHEMISTRY, Issue 7 2005
Jaromír Tou
Abstract The 1H and 13C NMR chemical shifts of cis - and trans -protopinium salts were measured and calculated. The calculations of the chemical shifts consisted of conformational analysis, geometry optimization (RHF/6,31G** method) and shielding constants calculations (B3LYP/6,31G** method). Based on the results of the quantum chemical calculations, two sets of experimental chemical shifts were assigned to the particular isomers. According to the experimental results, the trans -isomer is more stable and its population is ,68%. Copyright © 2005 John Wiley & Sons, Ltd. [source]