The hydrogen coverage of interstellar PAHs (Polycyclic Aromatic Hydrocarbons)
The rate at which the CH bond in interstellar Polycyclic Aromatic Hydrocarbons (PAHs) rupture due to the absorption of a uv photon has been calculated. The results show that small PAHs (less than or equal to 25 carbon atoms) are expected to be partially dehydrogenated in regions with intense uv fields, while large PAHs (greater than or equal to 25 atoms) are expected to be completely hydrogenated in those regions. Because estimate of the carbon content of interstellar PAHs lie in the range of 20 to 25 carbon atoms, dehydrogenation is probably not very important. Because of the absence of other emission features besides the 11.3 micrometer feature in ground-based 8 to 13 micrometer spectra, it has been suggested that interstellar PAHs are partially dehydrogenated. However, IRAS 8 to 22 micrometer spectra of most sources that show strong 7.7 and 11.2 micrometer emission features also show a plateau of emission extending from about 11.3 to 14 micrometer. Like the 11.3 micrometer feature, this new feature is attributed to the CH out of plane bending mode in PAHs. This new feature shows that interstellar PAHs are not as dehydrogenated as estimated from ground-based 8 to 13 micrometer spectra. It also constrains the molecular structure of interstellar PAHs. In particular, it seems that very condensed PAHs, such as coronene and circumcoronene, dominate the interstellar PAH mixture as expected from stability arguments.
- Research Organization:
- National Aeronautics and Space Administration, Moffett Field, CA (USA). Ames Research Center; Michigan Univ., Ann Arbor (USA). Dept. of Atmospheric and Oceanic Science; California Univ., Berkeley (USA). Radio Astronomy Lab.
- DOE Contract Number:
- FG02-85ER13442
- OSTI ID:
- 7131527
- Report Number(s):
- CONF-8602110-2; ON: DE87003376
- Resource Relation:
- Conference: Conference on polycyclic aromatic hydrocarbons and astrophysics, Les Houches, France, 1 Feb 1986
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
GENERAL PHYSICS
POLYCYCLIC AROMATIC HYDROCARBONS
INTERSTELLAR SPACE
PHOTONUCLEAR REACTIONS
EXPERIMENTAL DATA
INFRARED SPECTRA
ULTRAVIOLET RADIATION
AROMATICS
DATA
ELECTROMAGNETIC RADIATION
HYDROCARBONS
INFORMATION
NUCLEAR REACTIONS
NUMERICAL DATA
ORGANIC COMPOUNDS
RADIATIONS
SPACE
SPECTRA
640105* - Astrophysics & Cosmology- Galaxies