Video Experimental Relacionado
Updated: Jul 14, 2026
09:40
Measurement and Analysis of Atomic Hydrogen and Diatomic Molecular AlO, C2, CN, and TiO Spectra Following Laser-induced Optical Breakdown
Published on: February 14, 2014
El polimorfismo en los granos de Al2O3 presolar de estrellas gigantes ramificadas asimptóticas
Rhonda M Stroud1, Larry R Nittler, Conel M O'D Alexander
1Code 6360, Naval Research Laboratory, Washington, DC 20375, USA. stroud@nrl.navy.mil
Science (New York, N.Y.)
|September 9, 2004
Resumen
Se analizaron granos presolares de óxido de aluminio (Al2O3) de estrellas gigantes ramificadas asimptóticas. Estos granos de polvo cósmico confirman que las estrellas producen tanto corindón como Al2O3 amorfo, lo que afecta nuestra comprensión de los primeros materiales del sistema solar.
Área de la Ciencia:
- Cosmoquímica es la cosmoquímica.
- La astroquímica es astroquímica.
- Evolución Estelar Evolución Estelar
Sus antecedentes:
- El óxido de aluminio (Al2O3) se detecta en las envolturas de estrellas de ramas gigantes asintóticas (AGB) ricas en O.
- Se predice que Al2O3 será el primer sólido en condensarse en estos entornos estelares.
Objetivo del estudio:
- Analizar las propiedades microstruturales e isotópicas de dos granos de Al2O3 presolar.
- Investigar las vías de formación y las variaciones estructurales de Al2O3 en las estrellas AGB.
Principales métodos:
- Análisis microestructural de los granos de Al2O3 presolar.
- Análisis isotópico de granos de Al2O3 presolar.
Principales resultados:
- Se identificaron dos estructuras de grano de Al2O3 distintas: corindón y amorfo.
- La presencia de ambas estructuras confirma que las estrellas AGB producen ambas fases.
- Las variaciones en el contenido de titanio (Ti) sugieren que Al2O3 puede condensarse sin agrupaciones de semillas de TiO2, pero Ti influye en la estructura cristalina.
Conclusiones:
- Las estrellas de AGB son productores confirmados tanto de corindón como de óxido de aluminio amorfo.
- La condensación de Al2O3 es posible sin TiO2, con Ti jugando un papel en la determinación de su estructura cristalina.
Videos de Conceptos Relacionados
01:46Oxidative Cleavage of Alkenes: Ozonolysis
In ozonolysis, ozone is used to cleave a carbon–carbon double bond to form aldehydes and ketones, or carboxylic acids, depending on the work-up.
Ozone is a symmetrical bent molecule stabilized by a resonance structure.
Ozone is a symmetrical bent molecule stabilized by a resonance structure.
01:13¹H NMR: Complex Splitting
A proton M that is coupled to a proton X results in doublet signals for M. However, NMR-active nuclei can be simultaneously coupled to more than one nonequivalent nucleus. When M is coupled to a second proton A, such as in styrene oxide, each peak in the doublet is split into another doublet.
Splitting diagrams or splitting tree diagrams are routinely used to depict such complex couplings. While drawing splitting diagrams, the splitting with the larger coupling constant is usually applied first.
Splitting diagrams or splitting tree diagrams are routinely used to depict such complex couplings. While drawing splitting diagrams, the splitting with the larger coupling constant is usually applied first.
01:29Mass Spectrometry: Branched Alkane Fragmentation
This lesson delves into the mass spectrometry of branched alkane fragmentation. Branched alkanes possess secondary or tertiary carbon atoms, which generate relatively stable carbocations if the cleavage occurs at the branching point. The high stability of carbocations drives the instant fragmentation of branched alkanes. Accordingly, the branched alkane's molecular ion peak is very weak or invisible in the mass spectra, especially in comparison to a linear alkane.
00:59Mass Spectrometry: Alkene Fragmentation
Alkenes lose one electron from the unsaturated π bond upon ionization and form stable molecular ions. Further fragmentation of alkenes occurs through three different reaction pathways. The most prominent fragmentation is the cleavage at the allylic position. The resultant allylic carbocation is resonance stabilized. In the mass spectra of terminal alkenes, this fragment appears at a mass-to-charge ratio of 41. In the internal alkenes, where there are two choices of allylic cleavage, the...
00:53Mass Spectrometry: Alkyne Fragmentation
The fragmentation of alkynes preferentially occurs at the carbon–carbon bond between the α and β carbon of the alkyne bond to generate a 3-propynyl cation (or propargyl cation). In terminal alkynes, there is the only type of fragmentation that yields the 3-propynyl cation. The unsubstituted 3-propynyl cation exhibits a peak at a mass-to-charge ratio of 39. In internal alkynes, the 3-propynyl cation is substituted. For example, 2-pentyne fragments into methyl-substituted 3-propynyl cation, which...
01:27π Molecular Orbitals of the Allyl Radical
Allyl radicals are three-carbon conjugated systems. They are readily formed as intermediates in halogenation reactions of alkenes involving the addition of halogen to the allylic carbon instead of the double bond. As seen in allyl cations and anions, each of the three sp2-hybridized carbon atoms in allyl radicals has an unhybridized p orbital. These orbitals combine to give three π molecular orbitals.
The allyl systems have identical molecular orbitals but differ in the number of π electrons.
The allyl systems have identical molecular orbitals but differ in the number of π electrons.