An experimental study of the organic molecules produced in cometary and interstellar ice analogs by thermal formaldehyde reactions

Results of an experimental study tracing thermal formaldehyde reactions in astrophysically relevant ices in dense molecular clouds are reported. The formaldehyde chemistry during warm-up of ices containing H2CO and one or more of the molecules H2O, CH3OH, CO, O2, and NH3 were monitored using IR spectroscopy. Conversion of H2CO into residues was observed to start at about 40 K for NH3:H2CO ices and at about 80 K in H2O-rich ices. A total of five different organic products of these reactions were distinguished: POM and reaction products of H2CO and H2O, CH3OH, and NH3. Given the measured reaction paths and efficiencies, it is estimated that on the order of 1 percent of the organics found in the coma of Comet P/Halley could have been produced by thermal formaldehyde reactions taking place in the nucleus.