The infrared spectrum of OH-compensated defect sites in C-doped MgO and CaO single crystals

Freund, Friedemann; Wengeler, H.

doi:10.1016/0022-3697(82)90131-7

Cited by 68 publications

(20 citation statements)

References 35 publications

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“…1. In the same IR study (17), evidence was obtained that solute CO 2 in the MgO matrix exists in a chemically reduced form, probably as formate anions, CO 2 2Ϫ , with C occupying Mg 2ϩ vacancy sites, and in an even more reduced form as CO Ϫ anions with C on interstitial sites. This finding led to the proposition that dissolution of CO 2 in solid matrix is accompanied by a redox conversion similar to Eq.…”

Section: Discussionmentioning

confidence: 87%

“…Details of this reaction were further elaborated through an IR study of MgO crystals (17) becomes observable, as demonstrated by Fig. 1.…”

Section: Discussionmentioning

confidence: 99%

“…Previously it had been shown by gas chromatographic techniques (1, 4) that, after drying, no solvents are retained, even on finely crushed single crystal powders. By measuring the CH intensities from a thick MgO crystal and then cutting the same crystal into several slices, it had been shown earlier (17) that the CH band strength correlates with the length of the optical path through the bulk, not with the number of surfaces, indicating that the signal came from COH entities in the bulk. All IR spectra (before and after heating) were recorded at 30°C, acquiring data during 20 scans over the range 400 -4000 cm…”

Section: Methodsmentioning

confidence: 99%

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Organic protomolecule assembly in igneous minerals

Freund

Staple

Scoville

2001

Proc. Natl. Acad. Sci. U.S.A.

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COH stretching bands, CH, in the infrared spectrum of single crystals of nominally high purity, of laboratory-grown MgO, and of natural upper mantle olivine, provide an ''organic'' signature that closely resembles the symmetrical and asymmetrical COH stretching modes of aliphatic OCH 2 units. The CH bands indicate that H2O and CO2, dissolved in the matrix of these minerals, converted to form H 2 and chemically reduced C, which in turn formed COH entities, probably through segregation into defects such as dislocations. Heating causes the COH bonds to pyrolyze and the CH bands to disappear, but annealing at 70°C causes them to reappear within a few days or weeks. Modeling dislocations in MgO suggests that the segregation of C can lead to C x chains, x ‫؍‬ 4, with the terminal C atoms anchored to the MgO matrix by bonding to two O ؊ . Allowing H2 to react with such Cx chains leads to [O2C(CH2)2CO2] or similar precipitates. It is suggested that such C xOHyOOz entities represent protomolecules from which derive the short-chain carboxylic and dicarboxylic and the medium-chain fatty acids that have been solvent-extracted from crushed MgO and olivine single crystals, respectively. Thus, it appears that the hard, dense matrix of igneous minerals represents a medium in which protomolecular units can be assembled. During weathering of rocks, the protomolecular units turn into complex organic molecules. These processes may have provided stereochemically constrained organics to the early Earth that were crucial to the emergence of life.

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Section: Discussionmentioning

confidence: 87%

“…Details of this reaction were further elaborated through an IR study of MgO crystals (17) becomes observable, as demonstrated by Fig. 1.…”

Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

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Organic protomolecule assembly in igneous minerals

Freund

Staple

Scoville

2001

Proc. Natl. Acad. Sci. U.S.A.

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“…Evidence had been presented (Freund & Wengeler 1982) that the weak OH band at 3560 cm À1 is coupled to a distinct, although very weak, band at 4150 cm À1 , which is due to the HÀH stretching mode, HH , of molecular H 2 in a solid matrix (Kriegler & Welch 1968). The HH band is highlighted in the inset in Figure 9b.…”

Section: A2 Solid Solutions With H 2 Omentioning

confidence: 91%

“…However, carbonate anions are energetically highly unfavorable to substitute in the MgO structure. Instead, the incorporation of CO 2 is thought to be coupled to an electron transfer from four O 2À onto C 4+ (Freund & Wengeler 1982), leading to two oxyanion complexes, a carboxy anion, plus a peroxy anion, each associated with an Mg 2+ vacancy. The important point is that this leads to a reduction of the carbon: In both defects, the double negative charge of the Mg 2+ vacancy is fully compensated (Freund & Wengeler 1982).…”

Section: A2 Solid Solutions With H 2 Omentioning

confidence: 99%

Solid Solution Model for Interstellar Dust Grains and Their Organics

Freund

2006

ApJ

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We present a dust grain model based on the fundamental principle of solid solutions. The model is applicable to the mineral (silicate) component of the dust in the interstellar medium (ISM ). We show that nanometer-sized mineral grains, which condense in the gas-rich outflow of late-stage stars or expanding gas shells of supernova explosions, do not consist of just high melting point oxides or silicates. Instead they form solid solutions with gas-phase components H 2 O, CO, and CO 2 that are omnipresent in environments where the grains condense. Through a series of thermodynamically well-understood solid-state processes, these solid solutions become ''parents'' of organic matter that precipitates inside the grains. Thus, the mineral dust grains and their organics become part of the same thermodynamically defined solid phase and, hence, physically inseparable. This model can account for many astronomical observations, which no prior model can adequately address, specifically: (1) Organics in the diffuse ISM are identified by a 3.4 m IR band, characteristic of aliphatic hydrocarbons composed of ÀCH 2 À and of ÀCH 3 groups. (2) The methylene-to-methyl ratio is nearly constant, implying a CH 2 :CH 3 ratio of $5:2. (3) The intensity ratio between the 9.7 and the 3.4 m band is nearly constant, implying a silicate-to-organics ratio of $10:1. (4) In dense clouds the complex 3.4 m band is replaced by a weak, featureless 3.47 m band. (5) Whereas silicate grains identified by their 9.7 m band tend to align in magnetic fields, grains with a strong 3.4 m organic signature do not tend to align.

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Isotopic Oxygen Exchange between Dioxygen and MgO Catalysts for Oxidative Coupling of Methane

Karasuda

Aika

1997

Journal of Catalysis

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The infrared spectrum of OH-compensated defect sites in C-doped MgO and CaO single crystals

Cited by 68 publications

References 35 publications

Organic protomolecule assembly in igneous minerals

Organic protomolecule assembly in igneous minerals

Solid Solution Model for Interstellar Dust Grains and Their Organics

Isotopic Oxygen Exchange between Dioxygen and MgO Catalysts for Oxidative Coupling of Methane

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