45 



species which initiate chains of reactions leading to formation of the 

 observed molecules. In this manner complex molecules and, perhaps 

 even interstellar grains, are constructed within the clouds. A list of 

 molecules observed in these interstellar clouds is given in table IV- 1. 

 At this writing, more than 50 species have been identified. Glycine, 

 since it is the simplest amino acid (the building blocks of protein), 

 is of obvious interest for the origin of life. To date, the search for it 

 in the interstellar clouds has been unsuccessful. Finally, in addition 

 to the species listed in table IV- 1, many other as yet unidentified 

 molecules appear to be present. 



Alternative schemes for synthesis exist. One of those is the sug- 

 gestion that the molecules are not formed in interstellar clouds but 

 rather are formed under relatively high temperatures and high- 

 density conditions, such as in primordial solar nebulae. Those 

 nebulae are clouds of more concentrated dust and gas that form from 

 interstellar clouds and directly spawn suns. Regardless of the model 

 chosen, examination of the compounds in table IV- 1 leads to two 

 important observations. First, the compounds are chemically diverse 

 and structurally complex. Second, many of them are also known to 

 be produced by abiotic synthesis experiments in the laboratory (see 

 chap. V). 



Clearly, the interstellar environment, as exotic and as seemingly 

 inimical to chemical reactions as it may appear at first consideration, 

 exhibits a rich chemistry which manifests itself in the production of 

 organic compounds that, for the most part, are familiar to the 



TABLE IV- 1.- SPECIES IN THE INTERSTELLAR MEDIUM 



