RADIATION CHEMISTRY OF CARBON AND NITROGEN COMPOUNDS IN H2O AND NH3 ICES ; RELEVANCE FOR CHEMICAL EVOLUTION IN SPACEReport as inadecuate




RADIATION CHEMISTRY OF CARBON AND NITROGEN COMPOUNDS IN H2O AND NH3 ICES ; RELEVANCE FOR CHEMICAL EVOLUTION IN SPACE - Download this document for free, or read online. Document in PDF available to download.



Abstract : Radiolysis and photolysis of ice and ice-mixtures lead to the formation of new chemical compounds. Preexisting chemical compounds can be changed by the interaction with radicals formed in the frozen matrices and by direct radiolysis. The actual product distribution in an icy substrate is a function of radiation dose fluence and dose rate flux. The reactivity of irradiated H2O-ice depends on the equilibrium concentration, the mobility and reaction velocity of H*, HO* HO2* radicals, electrons, etc. The nuclear recoil process 1,2 offers an elegant method to introduce carrier-free probes without disturbing the macroscopic composition of the matrix. The kind of products formed by the radioactive atom is indicative for the redox properties of the ice. The accompanying radiation, e.g. of protons to induce the 14Np,α11C process in NH3 or the 16Op,αpn11C in H2O, allows to modify the radiation load. Fig. 1 shows the typical behaviour of 11C products in H2O-ice at 77 K as a function of the deposited proton dose 2. A neutral phase at low doses is characterized by relatively constant yields of the major products CH2O, CH3OH and CO2. It is followed by a reducing phase at medium dose CH3OH increase and an oxidizing phase at higher dose CO2 becomes the only product.





Author: B. Nebeling K. Rössler

Source: https://hal.archives-ouvertes.fr/



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