Theoretical study of the thermochemistry of fluorosilanes (SiFn and SiHnFm) compounds and hexafluorodisilane

Ho, Pauline; Melius, Carl F.

doi:10.1021/j100375a066

Cited by 177 publications

(143 citation statements)

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“…15,16 Thus, for finite temperatures, the raw G2 energies (without BAC corrections) obtained from the BAC-G2 method do not correspond to those from the output of a Gaussian G2 calculation, since hindered rotors are included in the BAC procedure.…”

Section: Introductionmentioning

confidence: 99%

“…Note that, in contrast to the original BAC-MP4 method, 15,16 in which the heat of formation for isolated atoms was set to the experimental value, the atomic heats of formation obtained from the BAC-G2 method differ somewhat from the experimental values. For example, the BACG2heat of formation for Al(g) is 80.144 kcal mol This difference results from the fact that the objective of the BAC-G2 method is to obtain accurate heats of formation for molecular species, which are the data most often needed for practical problems.…”

Section: Introductionmentioning

confidence: 99%

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BAC-G2 Predictions of Thermochemistry for Gas-Phase Aluminum Compounds

et al. 2002

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A self-consistent set of thermochemical data for 55 molecules in the Al-H-C-O-F-Cl system are obtained from ab initio quantum-chemistry calculations using the BAC-G2 method. Calculations were performed for both stable and radical species. Good agreement is found between the calculations and experimental heats of formation in most cases where data are available for comparison. Electronic energies, molecular geometries, moments of inertia, and vibrational frequencies are provided in the Supporting Information, as are polynomial fits of the thermodynamic data (heat of formation, entropy, and heat capacity) over the 300-3000 K temperature range. (This page intentionally left blank)5

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

BAC-G2 Predictions of Thermochemistry for Gas-Phase Aluminum Compounds

et al. 2002

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“…Allendorf and Melius 10 have calculated heats of formation of Cl 3 SiSiCl and Cl 2 SiSiCl 2 using the BAC-MP4 methodology. Bell et al 11 calculated energies for all of the chlorinated silylsilylenes and disilenes using the semiempirical MOBI method.…”

Section: Introductionmentioning

confidence: 99%

“…For reactions producing SiH, the endothermicity increases from 62 kcal/mol for H 3 SiSiH f SiH 3 + SiH to 67 kcal/mol for Cl 3 SiSiH f SiCl 3 + SiH. Likewise, for reactions producing SiCl, the endothermicity increases from 58 kcal/mol for H 3 -SiSiCl f SiH 3 + SiCl to 64 kcal/mol for Cl 3 SiSiCl f SiCl 3 + SiCl.…”

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confidence: 98%

Ab Initio Molecular Orbital Study of the Thermochemistry and Reactions of the Chlorinated Disilenes and Their Isomers (Si₂H_nCl_4-n)

Swihart

Carr

1998

J. Phys. Chem. A

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Structures, vibrational frequencies, and energies for the chlorinated disilenes, their dibridged isomers, and the transition states connecting the chlorinated disilenes to the corresponding silylsilylenes are presented. Geometries and frequencies were obtained at the MP2/6-31G(d,p) level, and energetics were calculated at the G2, G2(MP2), MP4/6-31+G(2df,p), and/or MP2/6-31+G(2df,p) levels of theory, depending on the number of chlorine atoms in the molecule. The silylsilylene isomer with the structure H n Cl 3-n SiSiCl was found to be lowest in energy for all of the chlorinated compounds. The dibridged structures are all significantly higher in energy than the silylsilylene and disilene structures. Barriers for isomerization by H transfer and Cl transfer ranged from 5 to 18 kcal/mol and 9 to 23 kcal/mol above the disilene, respectively. Energies along paths for decomposition of the chlorinated disilenes to pairs of silylenes are presented, confirming that the reverse reactions are barrierless. Finally, energetics of various decomposition products of the Si 2 H n Cl 4-n compounds are considered. It is shown that for the species with two or more chlorines, decomposition to a pair of silylenes should be the dominant reaction path based on the energetics of competing paths. The isomerization barriers are much smaller than decomposition barriers, so the isomerization reactions will be fast compared to decomposition.

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“…42,43 As shown in Figure 1c, the TS optimized with BH&HLYP/6-31G-(d) is much earlier along the reaction path than the TS optimized with MP2(full)/6-31G(d) (R C-C ) 2.823 vs 2.538 Å, R C-Cl ) 1.893 vs 1.988 Å), and the barrier from the reactant complex 44,45 Bond additivity corrections (BACs) have been used to improve the calculation of thermochemistry. [46][47][48][49][50] Even though this is very efficient for getting more accurate reaction enthalpies, it appears not to have been used previously in molecular dynamics calculations. Early forms of bond additivity corrections used only constants, 48 but subsequent work showed that better performance could be obtained with bond additivity corrections that are a function of the bond length.…”

Section: Resultsmentioning

confidence: 99%

A Single Transition State Serves Two Mechanisms. The Branching Ratio for CH₂O^•- + CH₃Cl on Improved Potential Energy Surfaces

Shaik

Schlegel

2006

J. Phys. Chem. A

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The reaction of formaldehyde radical anion with methyl chloride, CH 2 O •-+ CH 3 Cl, is an example in which a single transition state leads to two products: substitution at carbon (Sub(C), CH 3 CH 2 O • + Cl -) and electron transfer (ET, CH 2 O + CH 3• + Cl -). The branching ratio for this reaction has been studied by ab initio molecular dynamics (AIMD). The energies of transition states and intermediates were computed at a variety of levels of theory and compared to accurate energetics calculated by the G3 and CBS-QB3 methods. A bond additivity correction has been constructed to improve the Hartree-Fock potential energy surface (BAC-UHF). A satisfactory balance between good energetics and affordable AIMD calculations can be achieved with BH&HLYP/6-31G(d) and BAC-UHF/6-31G(d) calculations. Approximately 200 ab initio classical trajectories were calculated for each level of theory with initial conditions sampled from a thermal distribution at 298 K at the transition state. Three types of trajectories were distinguished: trajectories that go directly to ET product, trajectories that go to Sub(C) product, and trajectories that initially go into the Sub(C) valley and then dissociate to ET products. The BH&HLYP/6-31G(d) calculations overestimate the number of nonreactive and direct ET trajectories because the transition state is too early. For the BH&HLYP and BAC-UHF methods, about one-third of the trajectories that initially go into the Sub(C) valley dissociate to ET products, compared to just over half with UHF/6-31G(d) in the earlier study. This difference can be attributed to a better value for the calculated energy release from the initial transition state and to an improved Sub(C) f ET barrier height with the BH&HLYP and BAC-UHF methods.

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Theoretical study of the thermochemistry of fluorosilanes (SiFn and SiHnFm) compounds and hexafluorodisilane

Cited by 177 publications

References 1 publication

BAC-G2 Predictions of Thermochemistry for Gas-Phase Aluminum Compounds

BAC-G2 Predictions of Thermochemistry for Gas-Phase Aluminum Compounds

Ab Initio Molecular Orbital Study of the Thermochemistry and Reactions of the Chlorinated Disilenes and Their Isomers (Si₂H_nCl_4-n)

A Single Transition State Serves Two Mechanisms. The Branching Ratio for CH₂O^•- + CH₃Cl on Improved Potential Energy Surfaces

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Theoretical study of the thermochemistry of fluorosilanes (SiFn and SiHnFm) compounds and hexafluorodisilane

Cited by 177 publications

References 1 publication

BAC-G2 Predictions of Thermochemistry for Gas-Phase Aluminum Compounds

BAC-G2 Predictions of Thermochemistry for Gas-Phase Aluminum Compounds

Ab Initio Molecular Orbital Study of the Thermochemistry and Reactions of the Chlorinated Disilenes and Their Isomers (Si2HnCl4-n)

A Single Transition State Serves Two Mechanisms. The Branching Ratio for CH2O•- + CH3Cl on Improved Potential Energy Surfaces

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Ab Initio Molecular Orbital Study of the Thermochemistry and Reactions of the Chlorinated Disilenes and Their Isomers (Si₂H_nCl_4-n)

A Single Transition State Serves Two Mechanisms. The Branching Ratio for CH₂O^•- + CH₃Cl on Improved Potential Energy Surfaces