Interstellar Clouds formation

There are, however, still some unsolved, important questions103 about this fundamental reaction, of great relevance in dense interstellar clouds, where it could well be the source of the C3H and C3 species detected there. These unsolved questions are (a) what is the branching ratio for formation of the two isomeric C3H species, Z-C3H and C-C3H, and how does it vary with Ec (b) How do the detailed reaction dynamics and the branching ratio for C3H and C3 formation vary with Ec ... 

A much more detailed and time-dependent study of complex hydrocarbon and carbon cluster formation has been prepared by Bettens and Herbst,83 84 who considered the detailed growth of unsaturated hydrocarbons and clusters via ion-molecule and neutral-neutral processes under the conditions of both dense and diffuse interstellar clouds. In order to include molecules up to 64 carbon atoms in size, these authors increased the size of their gas-phase model to include approximately 10,000reactions. The products of many of the unstudied reactions have been estimated via simplified statistical (RRKM) calculations coupled with ab initio and semiempirical energy calculations. The simplified RRKM approach posits a transition state between complex and products even when no obvious potential barrier... 

The formation of stars in the interiors of dense interstellar clouds affects the chemistry of the immediate environment in a variety of ways depending on many factors such as the stage in the evolution of star formation, the mass of the star or protostar, and the density and temperature of the surrounding material. In general, the dynamics of the material in the vicinity of a newly forming star are complex and show many manifestations. Table 3 contains a list of some of the better studied such manifestations, which tend to have distinctive chemistries. These are discussed individually below. 

The evolution of a star from collapse of an interstellar cloud, through formation of the star to the supernova and the ejection of matter back into the interstellar medium... 

Today it is impossible to say whether prebiological evolution may have occurred in space, but for the moment there is no reason to exclude this option. Whatever hypotheses are retained, they must surely focus on the warmer regions (if we may use this word ) of the interstellar clouds, the very regions where star formation occurs. However, intense astrophysical searches for the simplest amino acid, glycine (NH2CH2COOH), in the dense cores of interstellar clouds have so far failed. 

Star formation and the formation of star systems with planets around them, constantly takes place in dense interstellar clouds. The material present in these clouds is incorporated into the objects that are formed during this process. Pristine or slightly altered organic matter from the cloud from which our solar-system was formed is therefore present in the most primitive objects in the solar system comets, asteroids, and outer solar-system satellites. Pieces of asteroids (and perhaps comets) can be investigated with regards to these components through the analyses of meteorites (and eventually in samples returned from these bodies by spacecraft) in laboratories on Earth. The infall of asteroid and comet material from space may have contributed to the inventory of organic compounds on primordial Earth. 

The aim of this article is to give a short outline of current theories of molecule formation and destruction in interstellar clouds, together with a short summary of the observational material which has been accumulated up to early 1981. Although this article will address itself predominantly to simple molecules a section on complex molecules has been added. We will, therefore, discuss some general aspects of cosmochemistry and then turn to molecule formation in diffuse clouds followed by a discussion of the chemistry of dense interstellar clouds. A section has been added to summarize recent observational results and theoretical proposals in understanding the formation of intermediate and complex molecules, an area of considerable current activity. Finally the article closes with a short summary of the molecular species found in planetary atmospheres and a short discussion of what the relation might be to the interstellar molecules. 

However, since we are dealing in this review primarily with problems related to star formation and galactic evolution, we shall ignore the work that has been done on dust formation and nucleation of classical (chemical) systems. These have been extensively reviewed by Abraham,Burton, and Draine and Salpeter for problems of astrophysical interest. We shall only refer to this literature for analogies which may be of some aid in establishing new directions for work on megascopic systems like interstellar clouds. 

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