Circumstellar Calcium Chemistry

2004 ◽  
Vol 57 (1) ◽  
pp. 67 ◽  
Author(s):  
Simon Petrie
Keyword(s):  
Dissociative Recombination ◽  
Molecular Ions ◽  
Bond Dissociation Energies ◽  
Circumstellar Envelopes ◽  
Loss Mechanism ◽  
Dissociation Energies ◽  
Mp2 Calculations ◽  
Circumstellar Environments ◽  
High Level ◽  
Recombination Reactions

High-level ab initio calculations are used to explore several aspects of calcium chemistry of direct relevance to formation and reaction of calcium-containing molecules in circumstellar envelopes. Counterpoise-corrected G2 and G2(MP2) calculations have been used to determine the bond dissociation energies (BDEs) of Ca+/NC2n+1H complexes (n = 0, 1, 2); these complexes, and CaNC7H+, are also assessed through counterpoise-corrected MP2(thaw)/6-311 + G(3df,2p) calculations. The relative energies of isomers of the feasible Ca(CN), Ca(C3N), and Ca(C5N) products (which may arise from dissociative recombination of the Ca+/NC2n+1H complexes) are obtained from G2 and G2(MP2) calculations; these calculations also permit evaluation of the thermochemistry of the dissociative recombination reactions in question. Thermochemical data are presented for a possible loss mechanism for calcium-containing neutrals by reaction with molecular ions in circumstellar envelopes. Finally, we provide an empirical assessment of the prospects for detecting the Ca(CN), Ca(C3N), and Ca(C5N) radicals within circumstellar environments.

Investigation Into Bio-Aviation Reaction Mechanisms Using Quantum Mechanical Methods

2008 ◽  
Author(s):  
Ida Shafagh ◽  
Kevin J. Hughes ◽  
Mohamed Pourkashanian ◽  
Alan Williams
Keyword(s):  
Rate Constants ◽  
Bond Dissociation Energies ◽  
Hydrogen Atoms ◽  
Dissociation Energies ◽  
Barrier Heights ◽  
Mechanical Methods ◽  
Methyl Butanoate ◽  
Level Model ◽  
Reactive Radicals ◽  
High Level

Using high level model chemistries the C-C and C-H bond dissociation energies for methyl butanoate molecule (MB) were estimated using the Gaussian 03 program at the CBS-QB3 level of calculations. This consequently located the weaker bonds more likely to break. Thermal decomposition of MB over the temperatures 500 to 2000 K was theoretically studied and the rate constants for these channels were calculated. Crucial reactions in combustion, among which there are reactions of the fuel molecule with flame reactive radicals OH and CH3, were studied and the barrier heights for reactions including different hydrogen atoms transferring to the radicals were evaluated at the B3LYP/6-31+G(d, p) level of theory. The rate constants for these reactions are calculated over the temperatures 500 to 2000 K using the same level.

O - H Bond Dissociation Energies

2011 ◽  
Vol 64 (4) ◽  
pp. 394 ◽  
Author(s):  
Bun Chan ◽  
Michael Morris ◽  
Leo Radom
Keyword(s):  
Density Functional ◽  
Cost Effective ◽  
Closed Shell ◽  
Bond Dissociation Energies ◽  
Functional Theory ◽  
Bond Dissociation ◽  
Dissociation Energies ◽  
Stabilization Energies ◽  
High Level ◽  
Precursor Molecules

High-level composite, ab initio and density functional theory (DFT) procedures have been employed to study O–H bond dissociation energies (BDEs), as well as radical stabilization energies (RSEs) in the oxygen-centred radicals that are formed in the dissociation of the O–H bonds. Benchmark values are provided by Wn results up to W3.2 and W4.x. We are able to recommend revised BDE values for FO–H (415.6 ± 3 kJ mol–1), MeC(O)O–H (459.8 ± 6 kJ mol–1) and CF3CH2O–H (461.9 ± 6 kJ mol–1) on the basis of high-level calculations. We find that Gn-type procedures are generally reliable and cost-effective, and that some contemporary functionals and double-hybrid DFT procedures also provide adequate O–H BDEs/RSEs. We note that the variations in the O–H BDEs are associated with variations in the stabilities of not only the radicals but also the closed-shell precursor molecules. Most substituents destabilize both species, with σ-electron-withdrawing groups having larger destabilizing effects, while π-electron acceptors are stabilizing. Although there is little correlation between the stabilizing/destabilizing effects of the substituents and the RSEs, we present some general patterns in the RSEs that emerge from the present study.

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