Chemical evolution interstellar space

Further increases in sensitivity and resolution of observational spectrometers will lead us to the detection of Hj in interstellar space. If detected, the spectrum will give crucial information on the working of the ion-neutral reaction scheme for the chemical evolution of molecular clouds. 

Galactic chemical evolution is the study of the evolution in time and space of the abundances of the chemical elements in the interstellar gas in galaxies. This process is influenced by many parameters such as the initial conditions, the star formation and evolution, the nucleosynthesis and possible gas flows. 

Further implications of the protosolar He/" He and D/H ratios are discussed by Gloeckler and Geiss (2000). The local interstellar cloud (LIC) represents a galactic sample having experienced chemical evolution for 4.6 Gyr longer than the protosun. D/H in the LIC is lower than the protosolar value whereas He/" e in the LIC is higher than the protosolar value (see also the Elementary particles in interplanetary space section). The direction of both these changes is expected, because stars only destroy deuterium but destroy and produce He. The observed increase of the He abundance is mainly due to production of this isotope in small stars. 

Cumulenes with ten or more cumulated carbon atoms have been detected in the interstellar space and some theories propose that such molecules played very important role in the formation of organic molecules during chemical evolution. 

In line with the spirit of this book, I will present mainly the highlights of our contributions and those of other laboratories on this subject, with autobiographical comments, following an approximate chronological order. I will leave aside the general aspects of the theory of chemical evolution and will mention briefly some of the more specific observations of organic molecules in interstellar space and comets. 

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