Solid organic residues produced by irradiation of hydrocarbon-containing H2O and H2O/NH3 ices: Infrared spectroscopy and astronomical implications

B. N. Khare, W. R. Thompson, B. G.J.P.T. Murray, C. F. Chyba, C. Sagan, E. T. Arakawa

Research output: Contribution to journalArticlepeer-review

38 Scopus citations


Methane clathrate (CH4· nH2O) - expected in cometary nuclei, in outer Solar System satellites, and perhaps in interstellar grains-aas well as ices prepared from other combinations of CH4, C2H6, or C2H2 with H2O (and sometimes with NH3) were irradiated at 77°K by plasma discharge. CH4 clathrate and other H2O/hydrocarbon ices color and darken noticeably after a dose ≈108 to ≈109 erg cm-2 over a period of 1-10 hr. Upon evaporation of the now yellowish to tan irradiated ices, a colored solid film adheres to the walls of the reaction vessel at room temperature. Transmission measurements of these organic films were made from 2.5 to 5μm wavelength. The residue left after CH4. irradiation exhibits IR bands which we tabulate and identify with alkane, aldehyde, alcohol, and perhaps alkene and substituted aromatic functional groups. Aldehydes are especially well indicated, and may be related to recent claims of polyoxymethylene in the coma of Comet Halley. Spectra presented here are compared with previous studies of UV or proton-irradiated, nonenclathrated hydrocarbon-containing ices and may be useful for interpreting infrared features found in the spectra of comets and interstellar grains.

Original languageEnglish (US)
Pages (from-to)350-361
Number of pages12
Issue number2
StatePublished - Jun 1989
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


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