Planetary destruction

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. 

Raman spectroscopy is a useful analytical technique for planetary exploration because it does not require sample manipulation, and macroscopic and microscopic analyses are possible when identifying components in the specimen. It is sensitive to organic and inorganic compounds and is not destmctive to samples that are strictly limited in quantity or accessibility and so they can be used afterwards for other, perhaps more destructive, analyses. In this respect the situation of a Raman spectrometer on a planetary rover or on a fixed lander, to which specimens are brought by a rover, are both acceptable space mission scenarios. 

Because of the ozone depletion that occurs by photolysis, the NO, break-even concentration at which net O, production occurs is somewhat larger than the value based just on the ratio of the rate constants of reactions 5.47 and 5.25. The approximate crossover point for NO, between O destruction and production is usually considered to be at about 30 ppt. Ozone mixing ratios in the planetary boundary layer over the remote Pacific Ocean are only about 5 to 6 ppb NO, levels are about 10 ppt. Thus, this region of the atmosphere is probably below the crossover point. 

The formation and destruction of N2H are important for understanding the chemistry of interstellar clouds, comets, and planetary atmospheres. It is generally assumed that the N2H ion in interstellar clouds arises mainly from the reactions H3-HN2- N2H +H2 and N2 + H2- N2H + H and that dissociative recombination N2H -he - N2H-H and proton transfer reactions with abundant interstellar species such as CO are the major loss processes see for example [11 to 15]. 

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