The genesis of the protoplanetary nebula from gas-dust interstellar clouds - Processes in interstellar gas

Literature data on the characteristics of Galactic gas-dust clouds are used to estimate the quantities of main elements in the protosolar nebula and the variations of molecular gas compositions in the process of collapse and during changes in P,T conditions. Data on the chemistry of dark molecular clouds indicate that, in the protosolar nebula, only gaseous hydrogen and nitrogen were present in molecular forms, while major fractions of oxygen, carbon, and sulfur constituted parts of dust particles. Molecules highly enriched in deuterium in dark molecular clouds were precursors of organic compounds encountered in chondrites and other solar-system bodies. Results on compositional changes of the protosolar nebula during its collapse and the accretion of the protoplanetary disk indicate that, during all stages of protosolar-nebula evolution, the molecular composition of the gas phase with high percentage of organic molecules changed due to changes in the P,T conditions, shock wave effects, UV irradiation, solar wind, and cosmic rays.