Molecules interstellar

The high-energy cosmic radiation, which consists of energy-rich protons, ionizes neutral atoms and molecules as it passes through the cosmos, for example, as follows  

These reactions take place very slowly under the extreme ultra-high vacuum conditions present in outer space, so that the chemistry is different to that observed in the laboratory. Thus there are still some open questions regarding the mysterious interstellar ion H3+, particularly with respect to its occurrence in diffuse clouds and its rate of decomposition (Suzor-Weiner and Schneider, 2001 Kokoruline et al., 2001). 

In the early days of biogenesis research, only the primeval Earth atmosphere was regarded as being the place where biomolecules or their precursors could have been formed (the Miller era). Later on, the Earth s surface and, after the discov- 

The detection of biomolecules in meteorite material, and of larger molecules in interstellar space, led to the assumption that the molecules required for biogenesis (or simple precursors for them) could have arrived on the young Earth from space. 

Several of the compounds identified in ISM have not so far been synthesized in the laboratory however, two of them have now been obtained. The cyclic compound cyclopropylidene (C3H2), first detected in ISM in 1985 and later more frequently, was considered to be too unstable to exist on Earth under laboratory conditions. A derivative of this carbocycle, stabilized by amino groups which serve as -donors, has now been reported. X-ray crystallography shows that the presence of the amino groups has little effect on the molecular geometry as calculated for the unsubstituted cyclopropylidene (Lavallo et al., 2006). 

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Interstellar molecules detected by their radiofrequency, microwave or millimetre wave spectra... 

First, it is not a common molecule on earth, not being used in laboratory for any synthesis. Second, it is cyclic, which was and still is a rare feature among small interstellar molecules identified up to day only SiCC and C3H present the same characteristic. 

C3H2 a puzzling interstellar molecule F. PauzatandD. Talbi... 

Table 1. Gas Phase Interstellar Molecules in Order of Increasing Complexity...

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. 

Recent studies with a crossed-beam apparatus not only show that the products shown above are the correct ones, but that both the linear and cyclic isomers, each of which is a detected interstellar molecule, are formed.47 Crossed-beam studies also show that other reactions between C atoms and unsaturated hydrocarbons proceed to form similar products 48... 

A second successful prediction is that many so-called metastable species (i.e. isomers) are abundant even if they are quite reactive in the laboratory.66 Perhaps the simplest interstellar molecule in this class is HNC, but large numbers of others can be seen in Table 1. It is assumed that most metastable species are formed in dissociative recombination reactions along with their stable counterparts at approximately equal rates, and that both are destroyed by ion-molecule reactions so that the laboratory reactivity, which is normally determined by reactions with neutral species, is irrelevant. Both HCN and HNC, for example, are thought to derive from the dissociative recombination reaction involving a linear precursor ion ... 

A fifth success concerns carbon monoxide, the dominant interstellar molecule from an observer s point of view. Despite all the uncertainties and problems with the model calculations, which will be amply brought out in this review, the predicted fractional abundance of CO is large and in the range of 10"5 to 10-4, in excellent agreement with observation. 

An extremely interesting question in the photochemistry of interstellar molecules concerns the size at which classes of molecules become resistant to the interstellar radiation field. Up to now, only statistical theories have been brought to bear on the question (see below).83 115... 

Lewis E. Snyder (2006) has reported on the importance and efficiency of interferometry for the study of complex (and in particular biochemically interesting) molecules in certain areas of ISM, such as interstellar molecule clouds. 

Binary ion-molecule reactions are indicated by thin arrows (c.t. indicates charge transfer), the radiative association reaction of C+ with H2 is indicated by the thick arrow and the dissociative recombination reactions are indicated by dashed arrows leading to the neutral molecules inside the compound brackets (e indicates free electrons). The molecules indicated in bold are known (observed) interstellar molecules. 

Kuan Y.-J., Chamley S. B., Huang H.-C., et al. (2004). Searches for interstellar molecules of potential prebiotic importance. Advances in Space Research 33 31. 

Interstellar molecules are grouped by their location in three types of clouds diffuse, dark, and black clouds [1]. The diffuse clouds are characterized by low gas density, predominately... 

The similarities in products and pathways between interstellar molecules and terrestrial laboratory experiments imply a unity of physical and chemical laws in the universe. Given certain conditions and appropriate energy sources, the same chemical pathways will be followed to create certain products from the elements. That is not to say that life, even in primitive form, could be supported in interstellar space. The significant precursor molecules found in interstellar space are at extremely low concentrations, but if they were transported to planetary atmospheres, perhaps by comets, they might then react in the proper environment and evolve into self-replicating systems. 

Recent microwave data for the potential interstellar molecule Sis is used together with high-level coupled-cluster calculations to extract an accurate equilibrium structure. Observed rotational constants for several isotopomers have been corrected for effects of vibration-rotation interaction subsequent least-squares refinements of structural parameters provide the equilibrium structure. This combined experimental-theoretical approach yields the following parameters for this C2v molecule re(SiSi) = 2.173 0.002A and 0e(SiSiSi) = 78.1 O.2 ... 

A hundred or so different molecular species have been spotted in molecular or circumstellar clouds. Most interstellar molecules are organic molecules, that is, they are carbon-based. This indicates that chemical evolution does occur on a cosmic scale. What is more, many molecules on the interstellar list are fundamental building-blocks for the construction of biological structures. 

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