Astromacromolecules: Formation of Very Large Molecules in Interstellar Space

Abstract

The study of the physical and chemical processes taking place in the interstellar medium is made possible by the creation of laboratory conditions which simulate those relevant in space - low temperature, ultra-high vacuum and the radiation field. For details of the experimental methods see Hagen et al.(1979). The irradiation of the icy mantles in the molecular cloud medium leads to the formation of refractory organic material on interstellar dust. The more soluble part of the laboratory photoproduced residues has been analysed by GCMS and HPLC (see e.g. Agarwal et al.(l986)). Recently we have performed analyses of the non-soluble part of the organic residue by pyrolysis chemical ionization mass spectrometry (PY-CIMS). For a description of this method see Pouwels et al.(1989) and Westmore and Alauddin (1986). Two examples of the PY-CIMS spectra of one of the samples starting with labelled and unlabelled mixtures are shown in figures 1 and 2. It should be noted that the labelled sample (fig. 2) was a residue left over from a residue analysed by GCMS - therefore there was very little material. The peaks are quite reproducible, and comparing the labelled and unlabelled samples, the shifts obviously indicate that the peaks we obtain are real and do not come from contamination; e.g., 69 shifts to 74, 83 to 89, and so on, depending on the number of carbons and nitrogens we have. All the samples consist of compounds of very high molecular weight - many (especially those with CH₄ and C₂H₂) with more than 500 mass peaks well above the background noise level (see figs. 1, 2 and 3). The arrow in the three figures indicates the maximum intensity of the base peak in the blank, i.e. all the peaks above the arrow are almost certainly real, and probably some of the peaks below it are real as well