Bonjour à tous,
Je suis débutant et j'ai un article de 81 de Eric Herbst qui prédit que l'on peut avoir des molécules négatives dans les nuages denses interstellaires, j'aimerai savoir pourquoi les molécules négatives ont été prédites il y a si longtemps mais observées en 2006 pour la première fois?!
Merci.
Bonlour,
Qu’entends-tu par molécule négative ? De l'antimatière ? Merci d'être un plus clair.
Connais toi toi-même (Devise de Socrate inspiré par Thalès)
Bonjour,
Une molécule ayant une charge négative, CN- , C3N- , etc bref des anions! Alors que des cations avaient déjà été observés.
Ah bon, merci, on appelle ça des ions; en passant C3N- ne seraisse pas plutôt NH3- ?
Connais toi toi-même (Devise de Socrate inspiré par Thalès)
A priori c'est que les anions sont en nombre beaucoup plus restreint que les cations.Envoyé par soso1022
http://media4.obspm.fr/public/AMC/pa...mpression.html
Mais je n'en connais pas la raison. Y'a un chercheur qui est sur la question :Une autre caractéristique de la composition chimique du MIS est la présence de cations (ions chargés positivement), et en particulier, de cations moléculaires, tels : CH+, SO+, H3 +, HCO+, HCS+, N2H+, H3O+, HOCO+, H2COH+, HCNH+, HC3NH+. Comme nous le verrons plus loin, les cations jouent un rôle fondamental dans la chimie interstellaire. Les anions (ions chargés négativement) sont aussi présents dans le MIS, mais en nombre beaucoup plus restreint.
Molecular Anions in the Laboratory and in Space
Michael C. McCarthy, Harvard University
The importance of negative ions (anions) in astronomy was demonstrated in 1939 by Rupert Wildt who showed that H– is the major source of optical opacity in the solar atmosphere, and therefore the material which one mainly sees when looking at the sun and similar stars. It is remarkable that in the many years since, during which nearly 130 neutral molecules and 14 positive molecular ions have been found in astronomical sources, no molecular anion has been identified. During the same period of time, more than 1000 molecular anions have now been studied in the laboratory at low resolution, but for only two diatomics, OH– and SH– , have rotational spectra been obtained. On the basis of recent experiments, a third negative molecular ion has been detected in the radio band in the laboratory, and, for the first time, in two wellknown astronomical sources as well: the molecular envelope of IRC+10216 and in the dense molecular cloud TMC-1. The new anion is a surprisingly molecule — the hexatriyne anion, C6H–, a carbon chain which is larger than nearly all the neutral molecules that have been found, and larger than all the cations. The present work suggests that a variety of other molecular anions may now be detectable in the laboratory and in space, and that some of these may be considerably easier to detect than one might suppose.Molecular Anions in the Laboratory and in Space
Michael C. McCarthy
Harvard Smithsonian Center for Astrophysics, Cambridge, USA The importance of negative ions (anions) in astronomy was demonstrated in 1939 by Rupert Wildt who showed that H¯ is the major source of optical opacity in the solar atmosphere, and therefore the material which one mainly sees when looking at the sun and similar stars. Despite the detection of many neutral and positively-charged molecules in space in the intervening 70 years, it was not until 2007 that a molecular anion (C6H¯) was identified for the first time in two rich astronomical sources on the basis of laboratory measurements of its rotational spectrum. Since that initial discovery, the closely-related carbon-chain anions, CCH¯, C4H¯, C8H¯, NCO¯, CN¯, and C3N¯ were subsequently detected in our laboratory; all but two of them have now been detected in space, and there is strong evidence for C5N¯ there as well, even thought its rotational spectrum has not yet been measured in the laboratory. The most readily observed anion, C6H¯, has now been detected in at least six other astronomical sources, suggesting that anions are probably widely distributed in the interstellar gas, often
present at the level of at least of few percent relative to the neutral parent. The high abundance of CN¯ relative to CN in the circumstellar shell of the evolved carbon star
IRC+10216, and the unexpected spatial distribution of C6H¯ relative to C6H in this source suggest that formation routes other than radiative electron attachment may be importan
Un conférence en anglais ici :
Michael C. McCarthy, "Molecular anions in the laboratory and in space"
ou ici :
Michael C. McCarthy, "Molecular anions in the laboratory and in space"
Dernière modification par Gilgamesh ; 22/06/2015 à 07h37.
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