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| Book/Report | FZJ-2018-02698 |
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1986
Kernforschungsanlage Jülich, Verlag
Jülich
Please use a persistent id in citations: http://hdl.handle.net/2128/18366
Report No.: Juel-2089
Abstract: The chemical consequences of implantation of 250 keV $^{12}$C$^{+}$ ions into 4-11 $\mu$m thick layers of solid NH$_{3}$ condensed from the gas phase have been studied at 8 K and 77. Carbon compounds such as CH$_{3}$ NH$_{2}$, CH$_{4}$ formamidine (or guanidine), CH$_{3}$ radicals, and N$_{2}$H$_{4}$ (as a radiolysis product of the matrix) were observed by means of IR-transmission spectroscopy in absorption. The detection of formamidine (or guanidine) as formed by reactions of hot carbon atoms is of special importance in view of the abiotic formation of organic compounds and precursors of biomolecules in ices and frozen volatiles in space. The condensation of formamidine or guanidine constitutes a major pathway to pyrimidine derivatives such as adenine, aminopyrimidines and finally nucleic acid bases. Thus, hot atom reactions may effectively contribute to chemical and biological evolution in the cosmos. The carbon ion implantation led to a high rate of sputtering of the NH$_{3}$ layer ranging from S = 400 to 3000 molecules per incident ion. Th large variation of S is due to differences in condensation and quality of the NH$_{3}$ layers. The number of carbon atoms (ions) the remaining layers of 0.5 to 6 $\mu$m was evaluated between 1.6 $\cdot$ 10$^{15}$ and 1.3 $\cdot$ 10$^{16}$ cm$^{-2}$. The total radiation dose (fluence) received by the remaining layer was between 60 and 270 eV per target molecule. That enabled a comparison with the results from the nuclear recoil method previously applied to the system $^{11}$C/NH$_{3}$ (s, 77K), which covers a similar dose range. The latter mehod allows studies of hot reactions at very low doses of radiation, but needs dissolving, melting, evaporation of the solid target prior to chromatographic analysis which may change the primary products, especially metastable species. Ion implantation together with optical spectroscopy is a true in-situ method, but needs some 10$^{15}$ to 10$^{16}$ implants cm for detection. This gives rise to high radiation doses and primary products are changed by radiolysis or radical attack. The good agreement between the results from both methods at medium high doses shows that the nuclear recoil method yields reliable data on products inthe solid state also in the low dose regime, where the true hot processes can be observed.
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