Stellar chemistry

Astrochemistry from astronomy to astrobiology. Andrew M. Shaw 2006 John Wiley Sons, Ltd 

At 2000 K there is sufficient energy to make the H2 molecules dissociate, breaking the chemical bond the core density is of order 1026 m-3 and the total diameter of the star is of order 200 AU or about the size of the entire solar system. The temperature rise increases the molecular dissociation, promoting electrons within the hydrogen atoms until ionisation occurs. Finally, at 106 K the bare protons are colliding with sufficient energy to induce nuclear fusion processes and the protostar develops a solar wind. The solar wind constitutes outbursts of material that shake off the dust jacket and the star begins to shine. 

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In 1868, a total solar ecHpse provided a unique oppoitunity to apply the spectroscope to stellar chemistry. At the moment when the Sun was perfectly eclipsed, the solar prominences surrounding the dark disk provided discrete line-emission spectra. Among these was a series of lines that matched no known elements. The discoverer, Joseph Norman Lockyer (1836-1920), postulated the existence of a new chemical element, helium after Helios (or Sun). The names of most metals typically end in ium or um and since most elements are metals hehum was first assumed to be a metal and named accordingly. Some 27 years later, helium was identified as a gas emanating from the uranium-containing mineral cleveite by William Ramsay. 

Anders, E., Hayatsu, R. (1981) Inter-stellar chemistry— polycyanoacetylene formation. Science, 214(4521), 689-... 

For a dozen years he regularly produced a series of immensely popular lectures on the latest discoveries in and applications of chemistry. Active in research, he discovered six elements in two years (1807-1808), conclusively disproved Lavoisier s hypothesis that oxygen was present in all acids (1810), and discovered and launched Michael Faraday into a stellar chemistry career. In 1812, he was knighted and in 1815 invented the coal miner s safety lamp that saved many lives. 

The astrochemistty of ions may be divided into topics of interstellar clouds, stellar atmospheres, planetary atmospheres and comets. There are many areas of astrophysics (stars, planetary nebulae, novae, supemovae) where highly ionized species are important, but beyond the scope of ion chemistry . (Still, molecules, including H2O, are observed in solar spectra [155] and a surprise in the study of Supernova 1987A was the identification of molecular species, CO, SiO and possibly ITf[156. 157]. ) In the early universe, after expansion had cooled matter to the point that molecules could fonn, the small fraction of positive and negative ions that remained was crucial to the fomiation of molecules, for example [156]... 

I have incurred many debts of gratitude to Prof E. J. Corey of Harvard University, who envisioned this project in the summer of 2002. What he once told me — The desire to learn is the greatest gift from God. —has been a true inspiration. Furthermore, it has been my greatest privilege as well as a pleasure to work with a stellar collection of contributing authors from both academia and industry. Some of them are world-renowned scholars in the field some of them have worked intimately with the name reactions that they have written some of them even took part in the discovery of the name reactions that they authored in this manuscript. As a consequence, this book truly represents the state-of-the-art for Name Reactions in Heterocyclic Chemistry. We will follow up with the second volume to complete the series on heterocyclic chemistry. 

The first question to ask about the formation of interstellar molecules is where the formation occurs. There are two possibilities the molecules are formed within the clouds themselves or they are formed elsewhere. As an alternative to local formation, one possibility is that the molecules are synthesized in the expanding envelopes of old stars, previously referred to as circumstellar clouds. Both molecules and dust particles are known to form in such objects, and molecular development is especially efficient in those objects that are carbon-rich (elemental C > elemental O) such as the well-studied source IRC+10216.12 Chemical models of carbon-rich envelopes show that acetylene is produced under high-temperature thermodynamic equilibrium conditions and that as the material cools and flows out of the star, a chemistry somewhat akin to an acetylene discharge takes place, perhaps even forming molecules as complex as PAHs.13,14 As to the contribution of such chemistry to the interstellar medium, however, all but the very large species will be photodissociated rapidly by the radiation field present in interstellar space once the molecules are blown out of the protective cocoon of the stellar envelope in which they are formed. Consequently, the material flowing out into space will consist mainly of atoms, dust particles, and possibly PAHs that are relatively immune to radiation because of their size and stability. It is therefore necessary for the observed interstellar molecules to be produced locally. 

The phosphorus chemistry occurring in interstellar matter and in the circum-stellar regions of the cosmos is not yet understood. We do, however, know that phosphorus compounds are present in meteorites, lunar rocks and Mars meteorites. Oddly enough, the element can be detected nearly everywhere, though only in low concentrations. Phosphate minerals, as well as the anions PO2 and PO3, have... 

The general extent of the molecular cloud can be mapped within the sky but the physical conditions and stellar activity lead to different chemical regimes, all of which must be considered if the chemistry of the ISM is to be understood. A... 

Introduction.—The identification of technetium in stars has been confirmed, thus establishing that stellar synthesis of this element is occurring. Recent developments in the analytical chemistries of technetium and rhenium have been reviewed, as has the extraction of rhenium from hydrochloric acid solutions a text describing the analytical chemistry of technetium and other man-made elements has been published. ... 

Lockyer s studies of the solar spectrum revealed to him that the sun is a miasma of chemical elements. Where did they come from In 1873 Lockyer developed the theory, later expounded in his Chemistry of the Sun (1887), that in the hottest (blue-white) stars the stellar matter is broken apart into the constituents of atoms themselves subatomieparticles, the protyle discussed by Dumas. Then, as the stars cooled, these particles combined to form regular elements - including some, like helium, not (then) known on Earth. 

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