Formaldehyde and Organic Molecule Production in Astrophysical Ices at Cryogenic Temperatures
Abstract
Thermally promoted formaldehyde (H_2CO) reactions in cryogenic ices have been studied to test their importance as a source of organic molecules in comets and interstellar ices. Ices containing H_2CO, H_2O, CH_3OH, CO, and NH_3 were investigated by using infrared spectroscopy. Small traces of NH_3 (NH_3/H_2CO >= 0.005) are sufficient to convert significant fractions (>= 40%) of the H_2CO into more complex organics. However, H_2CO reactions do not proceed without NH_3. Spectral evidence for reaction onset appeared between 40 and 80 kelvin, depending on the ice. Five distinct products were formed. These principally consist of polyoxymethylene and related derivatives. Polyoxymethylene itself was not made in significant amounts in cometary analogs. These products differ from those produced by ultraviolet and particle irradiation. The nature and relative amounts of the products depend on the initial composition, making these materials excellent tracers of a comet's history. About 3% of the organics in p-Halley's coma could have been produced by thermal H_2CO reactions.
- Publication:
-
Science
- Pub Date:
- February 1993
- DOI:
- 10.1126/science.11540093
- Bibcode:
- 1993Sci...259.1143S
- Keywords:
-
- Comets;
- Cryogenic Temperature;
- Formaldehyde;
- Ice;
- Infrared Spectroscopy;
- Interstellar Matter;
- Halley'S Comet;
- Organic Compounds;
- Astrophysics; Comets;
- COMETS;
- ICE;
- FORMALDEHYDE;
- ORGANIC MATERIAL;
- TEMPERATURE;
- MOLECULES;
- ORIGIN;
- SOURCE;
- LABORATORY STUDIES;
- SPECTROSCOPY;
- AMMONIA;
- SPECTRA;
- EXPERIMENTS;
- POLYOXYMETHYLENE;
- ANALOGS;
- INFRARED;
- WAVELENGTHS;
- WATER;
- CHEMISTRY;
- COMET NUCLEI;
- CARBON MONOXIDE;
- METHYL ALCOHOL;
- HALLEY;
- EMISSIONS