|dc.description.abstract||Carbon-rich meteorites and carbonaceous chondrites are found to contain many biologically relevant organic molecules. The presence of nucleobases (building block of DNA and RNA) in carbonaceous chondrites indicates that molecules of biological components can be formed in non-terrestrial environments via abiotic pathways. Recent laboratory experiments and ab initio calculations had already shown that the VUV irradiation of pyrimidine in H2O ices leads to the formation of oxidized pyrimidine derivatives, including the nucleobase uracil.
In this study, we focus on the different photo-energy effect on photon irradiation of pyrimidine in H2O-rich ice mixtures under astrophysical conditions (<10-9 torr, 14K).The vacuum ultra-violet (VUV) and extreme ultra-violet (EUV) photons provide by microwave-discharged hydrogen-flowed lamp (MDHL) and synchrotron radiation in several ranges: VUV (114−180 nm), 0th order light of synchrotron radiation beamline (25−300 nm), He I (58.4 nm), He II (30.4 nm). The photo-destruction rate of pyrimidine and photo-production rate of products were measured by FTIR spectroscopy. Afterwards, the photo-irradiated samples were warmed up to room temperature and the residues were analyzed by liquid and gas chromatography all together.
The results show that pyrimidine was easy to be depleted by VUV/ EUV photons, and formed many interstellar molecules such as: CO, CO2, HNCO, OCN-, CN-, H2CO, HCONH2, etc. All the photo-products in our experiments evidenced that 4(3H)-pyrimidone and uracil could be conclusively identified. The photo-destruction rate of pyrimidine and photo-production rate of products are found photon energy dependent. These results illustrate that the prebiotic components can be formed and survive in astrophysical environments which is subjected to VUV/EUV irradiation constantly. Finally they can be wrapped by H2O-rich ice matrix and fall down to Earth’s surface.