Theoretical Study on the Mechanism of Reaction of Ground-State Fe Atoms with Carbon Dioxide

2004 ◽  
Vol 69 (1) ◽  
pp. 13-33 ◽  
Author(s):  
Dimitrios A. Pantazis ◽  
Athanassios C. Tsipis ◽  
Constantinos A. Tsipis
Keyword(s):  
Ground State ◽  
Density Functional ◽  
Activation Barrier ◽  
Spectroscopic Properties ◽  
Basis Sets ◽  
Stationary Points ◽  
Insertion Reaction ◽  
Weakly Bound ◽  
Satisfactory Description ◽  
Bonding Properties

Density functional calculations at the B3LYP level of theory, using the 6-31G(d) and 6-311+G(3df) basis sets, provide a satisfactory description of the geometric and energetic reaction profile of the Fe + CO2 → FeO + CO reaction. The reaction is predicted to be endothermic by 23.24 kcal/mol at the B3LYP/6-311+G(3df)//B3LYP/6-31G(d) level of theory and to proceed by formation of either a Fe(η2-OCO) or a Fe(η3-OCO) intermediate. The Fe(η2-OCO) intermediate in the 5A' ground state is weakly bound with respect to Fe(5D) and CO2 dissociation products by 0.78 (2.88) kcal/mol at the B3LYP/6-31G(d) (B3LYP/6-311+ G(3df)//B3LYP/6-31G(d)) levels of theory. In contrast, the Fe(η3-OCO) intermediate in the 5A1 ground state is unbound with respect to Fe(5D) and CO2 dissociation products by 8.27 (11.15) kcal/mol at the same levels of theory. However, both intermediates are strongly bound relative to the separated Fe+(6D) and [CO2]- anion; the computed bond dissociation energies for the Fe(η2-OCO) and Fe(η3-OCO) intermediates are 207.33 and 198.28 kcal/mol in terms of ∆E0 at the B3LYP/6-31G(d), respectively. In the Fe(η2-OCO) and Fe(η3-OCO) intermediates, an intramolecular insertion reaction of the Fe atom to O-C bond takes place yielding the isomeric OFe(η1-CO) and OFe(η1-OC) products, respectively, with a relatively low activation barrier of 25.24 (21.69) and 26.36 (23.38) kcal/mol at the B3LYP/6-31G(d) (B3LYP/6-311+G(3df)//B3LYP/6-31G(d)) levels of theory, respectively. The calculated structures, relative stability and bonding properties of all stationary points are discussed with respect to computed electronic and spectroscopic properties, such as charge density distribution and harmonic vibrational frequencies.

Density Functional Study of the Electronic Structure and Related Properties of Pt(NO)/Pt(NO2) Redox Couples

2003 ◽  
Vol 68 (3) ◽  
pp. 423-446 ◽  
Author(s):  
Paraskevas Karipidis ◽  
Athanassios C. Tsipis ◽  
Constantinos A. Tsipis
Keyword(s):  
Ground State ◽  
Density Functional ◽  
Activation Barrier ◽  
Spectroscopic Properties ◽  
Redox Couple ◽  
Basis Set ◽  
Stationary Points ◽  
Functional Study ◽  
Dft Theory ◽  
Exothermic Process

Density functional calculations at the B3LYP level of theory, using the SDD basis set, provide satisfactory description of geometric, energetic, electronic and spectroscopic properties of the Pt(NO)/Pt(NO2) redox couple. The neutral Pt(NO) species adopts a bent 2A' ground state, while the cationic [Pt(NO)]+ species adopts a linear 1Σ+ ground state. The B3LYP/SDD- predicted Pt-N bond lengths are 2.016 and 1.777 Å for Pt(NO) (2A') and [Pt(NO)]+ (1Σ+), respectively, while the ∠Pt-N-O bent angle for [Pt(NO)] (2A') is 119.6°. On the other hand, the anionic [Pt(NO)]- species adopts the bent 1A' ground state with a Pt-N bond length of 1.867 Å and a ∠Pt-N-O bent angle of 122.5°. The computed binding energies of the NO, NO+ and NO- ligands with Pt(0) were found to be 29.9 (32.8), 69.9 (78.4) and 127.4 (128.7) kcal/mol at the B3LYP/SDD and CCSD(T)/SDD (numbers in parentheses) levels of theory, respectively. Moreover, the structure of the [Pt(NO2)]+ component of the Pt(NO)/Pt(NO2) redox couple and its transformation to [Pt(NO)]+ upon reaction with CO was analysed in the framework of the DFT theory. The coordination of the CO ligand to [Pt(NO2)]+ affords the cationic mixed-ligand [Pt(CO)(NO2)]+ complex, which is stabilized by 66.6 (60.5) kcal/mol, with respect to the separated [Pt(NO2)]+ and CO in their ground states. The O-transfer reaction from the coordinated NO2 to the coordinated CO ligands in the presence of the [Pt(NO2)]+ species corresponds to an exothermic process; the heat of the reaction (∆RH) is -85.2 (-80.5) kcal/mol and the activation barrier amounts to 27.7 (33.0) kcal/mol. Finally, the equilibrium structures of selected stationary points related to the transformation of NO to NO2 ligand located on the potential energy surfaces of the [Pt(NO),O2], [Pt(NO)+,O2], and [Pt(NO)-,O2] systems were analysed in the framework of the DFT theory. The computed interaction energies of O2 with Pt(NO), [Pt(NO)]+ and [Pt(NO)]- species were found to be 106.9 (105.3), 49.2 (48.4) and 26.9 (26.5) kcal/mol, respectively. The O2 ligand is coordinated to the Pt central atom in an end-on mode for [Pt(NO),O2] and [Pt(NO)-,O2] systems and in a side-on mode for the [Pt(NO)+,O2] system. The transformation of NO to NO2 in [Pt(NO)]- species upon reaction with dioxygen corresponds to an exothermic process; the heat of the reaction (∆RH) is -60.6 (-55.8) kcal/mol, while the activation barrier amounts to 35.5 (30.2) kcal/mol. Calculated structures, relative stability and bonding properties of all stationary points are discussed with respect to computed electronic and spectroscopic properties, such as charge density distribution and harmonic vibrational frequencies.

Quantum chemical B3LYP/cc-pvqz computation of ground-state structures and properties of small molecules with atoms of Z ≤ 18 (hydrogen to argon)(IUPAC Technical Report)

2001 ◽  
Vol 73 (9) ◽  
pp. 1521-1553 ◽  
Author(s):  
Rudolf Janoschek
Keyword(s):  
Small Molecules ◽  
Ground State ◽  
Quantum Chemical ◽  
Density Functional ◽  
Spectroscopic Properties ◽  
Computational Method ◽  
Coupling Constants ◽  
Basis Sets ◽  
General Question ◽  
Absolute Deviation

Since density functional theory (DFT) achieved a remarkable break-through in computational chemistry, the important general question "How reliable are quantum chemical calculations for spectroscopic properties?" should be answered anew. In this project, the most successful density functionals, namely the Becke B3LYP functionals, and the correlation-consistent polarized valence quadruple zeta basis sets (cc-pvqz) are applied to small molecules. In particular, the complete set of experimentally known diatomic molecules formed by the atoms H to Ar (these are 214 species) is uniformly calculated, and calculated spectroscopic properties are compared with experimental ones. Computationally demanding molecules, such as open-shell systems, anions, or noble gas compounds, are included in this study. Investigated spectroscopic properties are spectroscopic ground state, equilibrium internuclear distance, harmonic vibrational wavenumber, anharmonicity, vibrational absolute absorption intensity, electric dipole moment, ionization potential, and dissociation energy. The same computational method has also been applied to the ground-state geometries of 56 polyatomic molecules up to the size of benzene. Special sections are dedicated to nuclear magnetic resonance (NMR) chemical shifts and isotropic hyperfine coupling constants. Each set of systems for a chosen property is statistically analyzed, and the above important question "How reliable...?" is mathematically answered by the mean absolute deviation between calculated and experimental data, as well as by the worst agreement. In addition to presentation of numerous quantum chemically calculated spectroscopic properties, a corresponding updated list of references for experimentally determined properties is presented.

Atomic-scale studies of chemical and transport processes relevant to propellant combustion

2018 ◽  
Author(s):  
◽  
Rezvan Chitsazi
Keyword(s):  
Ground State ◽  
Density Functional ◽  
Minimum Energy ◽  
Transport Processes ◽  
Electronic Ground State ◽  
Atomic Scale ◽  
Stationary Points ◽  
Insertion Reaction ◽  
Electronic Ground ◽  
Minimum Energy Pathway

[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT AUTHOR'S REQUEST.] Density functional theory (DFT) and correlated molecular orbital electronic structure calculations were used to study the Al + CO2 [subscript arrow] AlO + CO reaction on the electronic ground-state potential-energy surface (PES). Geometries were optimized using DFT (M11/jun-cc-pV(Q+d)Z) and more accurate energies were obtained using the composite Weizmann-1 theory with Brueckner doubles (W1BD). The results comprise the most complete, most systematic characterization of the Al + CO2 reaction surface to date and are based on consistent application of high-level methods for all stationary points identified. The pathways from Al + CO[subscript 2] to AlO + CO on the electronic ground-state PES all involve formation of one or more stable AlCO2 complexes denoted ?-AlCO2, trans-AlCO[subscript 2], and C[subscript 2v]-AlCO[subscript 2], among which [subscript n]-AlCO[subscript 2] and C[subscript 2v]-AlCO[subscript 2] are the least and most stable, respectively. We report a new minimum-energy pathway for the overall reaction, namely formation of [subscript n]-AlCO[subscript 2] from reactants and dissociation of that same complex to products via a bond-insertion reaction that passes through a fourth (weakly metastable) AlCO[subscript 2] complex denoted cis-OAlCO. Natural Bond Orbital analysis was applied to study trends in charge distribution and the degree of charge transfer in key structures along the minimum-energy pathway. The process of aluminum insertion into CO[subscript 2] is discussed in the context of analogous processes for boron and first-row transition metals. ...

scholarly journals Direct Kinetic Measurements and Master Equation Modelling of the Unimolecular Decomposition of Resonantly-Stabilized CH2CHCHC(O)OCH3 Radical and an Upper Limit Determination for CH2CHCHC(O)OCH3 + O2 Reaction

2020 ◽  
Vol 234 (7-9) ◽  
pp. 1251-1268 ◽  
Author(s):  
Satya Prakash Joshi ◽  
Prasenjit Seal ◽  
Timo Theodor Pekkanen ◽  
Raimo Sakari Timonen ◽  
Arrke J. Eskola
Keyword(s):  
Master Equation ◽  
Density Functional ◽  
Rate Coefficient ◽  
Decomposition Kinetics ◽  
Basis Sets ◽  
Stationary Points ◽  
Unimolecular Decomposition ◽  
Kinetic Measurements ◽  
Point Energy ◽  
Upper Limit

AbstractMethyl-Crotonate (MC, (E)-methylbut-2-enoate, CH3CHCHC(O)OCH3) is a potential component of surrogate fuels that aim to emulate the combustion of fatty acid methyl ester (FAME) biodiesels with significant unsaturated FAME content. MC has three allylic hydrogens that can be readily abstracted under autoignition and combustion conditions to form a resonantly-stabilized CH2CHCHC(O)OCH3 radical. In this study we have utilized photoionization mass spectrometry to investigate the O2 addition kinetics and thermal unimolecular decomposition of CH2CHCHC(O)OCH3 radical. First we determined an upper limit for the bimolecular rate coefficient of CH2CHCHC(O)OCH3 + O2 reaction at 600 K (k ≤ 7.5 × 10−17 cm3 molecule−1 s−1). Such a small rate coefficient suggest this reaction is unlikely to be important under combustion conditions and subsequent efforts were directed towards measuring thermal unimolecular decomposition kinetics of CH2CHCHC(O)OCH3 radical. These measurements were performed between 750 and 869 K temperatures at low pressures (<9 Torr) using both helium and nitrogen bath gases. The potential energy surface of the unimolecular decomposition reaction was probed at density functional (MN15/cc-pVTZ) level of theory and the electronic energies of the stationary points obtained were then refined using the DLPNO-CCSD(T) method with the cc-pVTZ and cc-pVQZ basis sets. Master equation simulations were subsequently carried out using MESMER code along the kinetically important reaction pathway. The master equation model was first optimized by fitting the zero-point energy corrected reaction barriers and the collisional energy transfer parameters $\Delta{E_{{\text{down}},\;{\text{ref}}}}$ and n to the measured rate coefficients data and then utilize the constrained model to extrapolate the decomposition kinetics to higher pressures and temperatures. Both the experimental results and the MESMER simulations show that the current experiments for the thermal unimolecular decomposition of CH2CHCHC(O)OCH3 radical are in the fall-off region. The experiments did not provide definite evidence about the primary decomposition products.

The Nearly Degenerate Triplet Electronic Ground State Isomers of Lithium Nitroxide

2007 ◽  
Vol 72 (2) ◽  
pp. 129-152 ◽  
Author(s):  
Justin M. Turney ◽  
Henry F. Schaefer
Keyword(s):  
Ground State ◽  
Global Minimum ◽  
Electronic Ground State ◽  
Basis Sets ◽  
Stationary Points ◽  
Mechanical Methods ◽  
State Potential ◽  
Correlation Consistent ◽  
Highly Correlated ◽  
Electronic Ground

The triplet electronic ground state potential energy surface of lithium nitroxide has been systematically investigated using convergent quantum mechanical methods. Equilibrium structures and physical properties for five stationary points (three minima and two transition states) have been determined employing highly correlated coupled cluster theory with four correlation-consistent polarized-valence (cc-pVXZ and aug-cc-pVXZ, X = T and Q) and two core correlation-consistent polarized-valence (cc-pCVXZ, X = T and Q) basis sets. The global minimum, roughly L-shaped Li-O-N, is predicted to lie 6.5 kcal mol-1 below the linear LiON minimum and 2.4 kcal mol-1 below the linear LiON minimum. The barrier to isomerization from the global minimum to LiON was found to be 7.4 kcal mol-1 and with regard to LiNO 6.9 kcal mol-1. The dissociation energies, D0, with respect to Li + NO, have been predicted for all minima and for the global minimum was found to be 34.9 kcal mol-1.

scholarly journals Computational studies of Ni(II) photosensitizers complexes containing 1,1′-bis(diphenylphosphino)ferrocene and dithio ligands

2020 ◽  
Vol 98 (4) ◽  
pp. 194-203 ◽  
Author(s):  
Sefia Brahim ◽  
Houari Brahim ◽  
Stéphane Humbel ◽  
Ali Rahmouni
Keyword(s):  
Density Functional Theory ◽  
Density Functional ◽  
Dye Sensitized Solar Cells ◽  
Substituent Effects ◽  
Spectroscopic Properties ◽  
Basis Sets ◽  
Functional Theory ◽  
Square Planar ◽  
Td Dft ◽  
Sensitized Solar Cells

Detailed theoretical studies of Ni(II) complexes in a distorted square planar form and containing dithio and (P, P) chelating ligands were performed. These Ni(II) complexes are investigated for their use in dye-sensitized solar cells (DSSC). Structures and UV–vis spectra are calculated at density functional theory (DFT) and time-dependent density functional theory (TD-DFT) theories using B3LYP and CAM-B3LYP functionals and 6-31G(d,p) and 6-31G+(d) basis sets. Geometry optimizations result in excellent agreement with the experimental results. Moreover, the analysis of the frontier molecular orbitals (FMOs) allowed a detailed assignment and a clear analysis of the electronic transitions. The TD-DFT calculations reproduce the main spectroscopic properties observed and substituent effects. The results reveal that all absorption spectra are characterized by mixed character mainly dominated by metal to ligand and ligand to ligand charge transfers (MLCT and LLCT). We unveil how the substituent variations affect the DSSCs features of the complexes.

Comparative DFT study on the α-glycosidic bond in reactive species of galactosyl diphosphates

2009 ◽  
Vol 63 (5) ◽  
Author(s):  
Juraj Kóňa ◽  
Igor Tvaroška
Keyword(s):  
Density Functional ◽  
Catalytic Mechanism ◽  
Activation Barrier ◽  
Reaction Pathway ◽  
Glycosidic Bond ◽  
Stationary Points ◽  
Correct Prediction ◽  
Sugar Phosphate ◽  
Dft Methods ◽  
Mp2 Method

AbstractCorrect prediction of the structure and energetics along the reaction pathway of the formation or dissociation of the glycosidic bond in sugar phosphates is crucial for the understanding of catalytic mechanism and for the determination of transition state structures of sugar-phosphate processing enzymes. The performance of seven density functional theory (DFT) methods (BLYP, B3LYP, MPW1PW91, MPW1K, MPWB1K, M05 and M05-2X) and two wave function methods (HF and MP2) was tested using four structural models with the activated sugar-phosphate α-glycosidic linkage. The models were chosen based on the crystal structure of the retaining glycosyltransferase LgtC complex with methyl α-d-galactopyranose diphosphate and its 2-fluoro derivative. Results of the MP2 method were used as a benchmark for the other methods. Two structural trends were observed in the calculations: predicted length of the activated C1-O1 glycosidic bond of 1.49–1.63 Å was significantly larger than values of a standard C1-O1 glycosidic bond in crystal structures of carbohydrates (1.39–1.48 Å), and the calculated value depended on the DFT method used. The MPW1K, M05 and M05-2X functionals provided results in closest agreement with those from the MP2 method, the difference being less than 0.02 Å in the calculated glycosidic bond lengths. On the contrary, the BLYP and B3LYP functionals failed to predict sugar diphosphate in the (-sc) conformation as a stable structure. Instead, the only stationary points localized along the C1-O1 dissociation coordinate were oxocarbenium ions at the distance of approximately 2.8 Å. The M05-2X, MPW1K and MPWB1K functionals gave the most reasonable prediction of the thermochemical kinetic parameters, where the formation of the oxocarbenium ion has a slightly endothermic character (0.4–1.7 kJ mol−1) with an activation barrier of 7.9–9.2 kJ mol−1.

Theoretical study on the reaction mechanism of vinyl acetate with OH radicals in the atmosphere

2013 ◽  
Vol 91 (4) ◽  
pp. 241-247 ◽  
Author(s):  
Yan Zhao ◽  
Haitao Sun ◽  
Renjun Wang ◽  
Fei Gao
Keyword(s):  
Vinyl Acetate ◽  
Potential Energy Surfaces ◽  
Density Functional ◽  
Theoretical Study ◽  
Single Point ◽  
Density Functional Theory Method ◽  
Basis Sets ◽  
Stationary Points ◽  
Oh Radicals ◽  
Point Energy

The reaction mechanisms of vinyl acetate with OH radicals in the atmosphere have been studied using the density functional theory method. The geometry parameters and frequencies of all of the stationary points are calculated at the MPWB1K level with the 6-31G(d,p) basis sets. The single-point energy calculations are carried out at the MPWB1K/6-311+G(3df,2pd) level. The detailed profiles of the potential energy surfaces for the reactions are constructed. Two OH addition and three H abstraction reaction pathways are considered for the reaction of vinyl acetate with OH radicals. The theoretical study shows that the most energetically favorable isomer is that of OH addition to the terminal carbon positions (C1 atom). The α-ester rearrangement, which is characteristic of ester oxidation processes, is confirmed to be thermodynamically and kinetically favorable. The main products of the OH-initiated atmospheric oxidation of vinyl acetate are formaldehyde, formic acetic anhydride, and acetic acid.

Theoretical Studies on the Structure and Spectroscopic Properties of 2,4-D (2,4-Diclorofenoxiacetic Acid)

2012 ◽  
Vol 2 (1) ◽  
pp. 1-11
Author(s):  
María G. Andino ◽  
Mariela I. Profeta ◽  
Jorge M. Romero ◽  
Nelly L. Jorge ◽  
Eduardo A. Castro
Keyword(s):  
Density Functional ◽  
Theoretical Calculations ◽  
Spectroscopic Properties ◽  
Uv Spectra ◽  
Basis Set ◽  
Basis Sets ◽  
Electronic Effects ◽  
B3lyp Method ◽  
Molecular Stability ◽  
2,4 Dichlorophenoxyacetic Acid

The 2,4-dichlorophenoxyacetic acid (2,4-D) is applied to and recovered from the leaf surfaces of garden bean and corn plants. This paper examines the theoretical study of the 2,4-D IR and UV spectra as well as the determination of its optimized molecular structure. Theoretical calculations are performed at the density functional theory (DFT) levels. The different structural and electronic effects determining the molecular stability of the conformers are discussed in a comparative fashion. The optimized geometry was calculated via the B3LYP method with 6-311G(d,p) and 6-311++G(d,p) basis sets and the FT-IR spectra was calculated by the density functional B3LYP method with the 6-311++G(d,p) basis set. The scaled theoretical wavenumbers show good agreement with the experimental values. A detailed interpretation of the infrared spectra of 2,4-D is reported.

A theoretical study of the 77Se NMR and vibrational spectroscopic properties of SenS8–n ring molecules

2002 ◽  
Vol 80 (11) ◽  
pp. 1435-1443 ◽  
Author(s):  
J Komulainen ◽  
R S Laitinen ◽  
R J Suontamo
Keyword(s):  
Ab Initio ◽  
Density Functional ◽  
Chemical Shifts ◽  
Atomic Orbital ◽  
Geometry Optimization ◽  
Spectroscopic Properties ◽  
Basis Sets ◽  
Orbital Method ◽  
Hybrid Functional ◽  
Ring Molecules

The structures and spectroscopic properties of SenS8–n ring molecules have been studied by the use of ab initio molecular orbital techniques and density functional techniques involving Stuttgart relativistic large core effective core potential approximation with double zeta basis sets for valence orbitals augmented by two polarization functions for both sulfur and selenium. Full geometry optimizations have been carried out for all 30 isomers at the Hartree-Fock level of theory. The optimized geometries and the calculated fundamental vibrations and Raman intensities of the SenS8–n molecules agree closely with experimental information where available. The nuclear magnetic shielding tensor calculations have been carried out by the Gauge-independent atomic orbital method at the DFT level using Becke's three-parameter hybrid functional with Perdew/Wang 91 correlation. The isotropic shielding tensors correlate well with the observed chemical shift data. The calculated chemical shifts provide a definite assignment of the observed 77Se NMR spectroscopic data and can be used in the prediction of the chemical shifts of unknown SenS8–n ring molecules.Key words: selenium sulfides, ab initio, DFT, effective core potentials, geometry optimization, energetics, fundamental vibrations, 77Se chemical shifts.

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