title: Pre-cometary ice composition from hot core chemistry.
abstract: Pre-cometary ice located around star-forming regions contains molecules that are pre-biotic compounds or pre-biotic precursors. Molecular line surveys of hot cores provide information on the composition of the ice since it sublimates near these sites. We have combined a hydrostatic hot core model with a complex network of chemical reactions to calculate the time-dependent abundances of molecules, ions, and radicals. The model considers the interaction between the ice and gas phase. It is applied to the Orion hot core where high-mass star formation occurs, and to the solar-mass binary protostar system IRAS 16293-2422. Our calculations show that at the end of the hot core phase both star-forming sites produce the same prebiotic CN-bearing molecules. However, in the Orion hot core these molecules are formed in larger abundances. A comparison of the calculated values with the abundances derived from the observed line data requires a chemically unprocessed molecular cloud as the initial state of hot core evolution. Thus, it appears that these objects are formed at a much younger cloud stage than previously thought. This implies that the ice phase of the young clouds does not contain CN-bearing molecules in large abundances before the hot core has been formed. The pre-biotic molecules synthesized in hot cores cause a chemical enrichment in the gas phase and in the pre-cometary ice. This enrichment is thought to be an important extraterrestrial aspect of the formation of life on Earth and elsewhere.
authors.affiliation: Institute of Planetary Research, DLR Berlin, Rutherfordstrasse 2, 12489 Berlin, Germany. Carmen.Tornow@dlr.de
authors.forename: Carmen
authors.initials: C
authors.lastname: Tornow
authors.forename: Ekkehard
authors.initials: E
authors.lastname: Kührt
authors.forename: Uwe
authors.initials: U
authors.lastname: Motschmann
mesh_terms: D000097:Acetonitriles / Q000138:chemical synthesis; D000641:Ammonia / Q000737:chemistry; D055580:Astronomical Phenomena; D001256:Astronomy; D055598:Chemical Phenomena; D002621:Chemistry; D005118:Extraterrestrial Environment; D006371:Helium / Q000737:chemistry; D006856:Hydrogen Cyanide / Q000138:chemical synthesis; D007053:Ice; D007700:Kinetics; D000432:Methanol / Q000737:chemistry; D008956:Models, Chemical
chemical_list: D000097:Acetonitriles; D007053:Ice; D006371:Helium; D006856:Hydrogen Cyanide; D000641:Ammonia; D000432:Methanol