| 1. |
- Fängström, Torbjörn, et al.
(författare)
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Density functional study of chlorine-oxygen compounds related to the ClO self-reaction
- 1998
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Ingår i: International Journal of Quantum Chemistry. - 0020-7608 .- 1097-461X. ; 66:3, s. 203-217
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Tidskriftsartikel (refereegranskat)abstract
- Geometrical parameters, vibrational frequencies, relative stabilities, and dissociation energies of the three stable Cl2O2 isomers and the OClO and ClOO radicals were investigated by density functional theory (DFT). The present analysis shows that DFT using hybrid functionals is capable of describing these systems to at least the same degree of accuracy as ab initio methods. The average absolute bond-length deviation of ClClO2,, ClOOCl, and ClO2, from experimental results is 0.024/0.027 Angstrom, with a maximum deviation for the dichlorine peroxide O-O bond equal to 0.072/0.063 Angstrom, for the B3PW91 and B3LYP functionals, respectively. The average absolute bond-angle deviation for the hybrid functionals is 0.8 degrees. Harmonic vibrational frequencies calculated with DFT give for all Cl-O compounds good agreement with experiments. The dissociation energies of ClOOCl, OClO, and ClOO were found to be in good agreement with experiments, the average error being less than 1.2 kcal/mol. The two isomers chloryl chloride (ClClO2,) and dichlorine peroxide (ClOOCl) were found to be approximately 9 kcal/mol more stable than the chlorine chlorite (ClOClO) isomer. The ClOO isomer is predicted to be 3.0 kcal/mol more stable than OClO, in accordance with the experimental value of 4 kcal/mol.
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| 2. |
- Garcia, Lopez Ramon J, et al.
(författare)
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Boron in very metal-poor stars
- 1998
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Ingår i: ASTROPHYSICAL JOURNAL. - : UNIV CHICAGO PRESS. - 0004-637X. ; 500:1, s. 241-256
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Tidskriftsartikel (refereegranskat)abstract
- We have observed the B I lambda 2497 line to derive the boron abundances of two very metal-poor stars selected to help in tracing the origin and evolution of this element in the early Galaxy: BD +23 degrees 3130 and HD 84937. The observations were conduct
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| 3. |
- Tomkin, Jocelyn, et al.
(författare)
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The rise and fall of the NaMgAl stars
- 1997
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Ingår i: ASTRONOMY AND ASTROPHYSICS. - 0004-6361. ; 327:2, s. 587-597
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Tidskriftsartikel (refereegranskat)abstract
- We have made new abundance determinations for a sample of NaMgAl stars. These stars, which are a subgroup of the nearby metal-rich field F and G disk dwarfs, were first identified by Edvardsson et al. (1993) on the basis of their apparent enrichment in Na, Mg and Al relative to other elements. The discovery of a planetary companion to the nearby solar type star 51 Peg (Mayor & Queloz 1995) combined with Edvardsson et al.'s earlier identification of 51 Peg as a NaMgAl star highlighted the group's potential importance. Our new analysis, which uses new spectra of higher resolution and better wavelength coverage than the analysis of Edvardsson et al., shows that the Na, Mg and Al abundances of the NaMgAl stars are indistinguishable from those of non-NaMgAl stars with otherwise similar properties. The group thus appears to be spurious.Our study, which includes 51 Peg, also provides the most complete set of abundances for this star available to date. The new Fe abundance, [Fe/H] = +0.20 +- 0.07, of 51 Peg confirms earlier measurements of its metal richness. Abundances for 19 other elements, including C, N and O, reveal a fairly uniform enrichment similar to that of Fe and show no evidence of abnormality compared to other metal rich stars of similar spectral type.
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