Astronomy and Astrophysics – Astronomy
Scientific paper
May 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009aas...21440213b&link_type=abstract
American Astronomical Society, AAS Meeting #214, #402.13; Bulletin of the American Astronomical Society, Vol. 41, p.664
Astronomy and Astrophysics
Astronomy
Scientific paper
We suggest that ethylene oxide (EO, c-C2H4O) and its isomers, acetaldehyde (AC, CH3CHO) and vinyl alcohol (VA, CH2CHOH) may be the source of the unidentified infrared bands (UIR) and their underlying continuum. Microwave transitions of all three isomers have been observed in many astronomical objects, all of which show the UIR bands. We show that the fundamental and overtone vibrational frequencies of EO correlate well with the major UIR bands at 3.3, 6.2, 7.7, 8.6, and 11.2 μm. Two additional UIR features at 12.7 and 16.4 μm are consistent with vibrationally excited EO, which is not collisionally quenched in space because the collision rate is negligible compared to the photon emission rate. In our mechanism, a vibrationally and rotationally cold AC molecule absorbs a 9 eV UV photon to produce vibrationally hot and rotationally cold AC in an excited electronic state. The excited AC either (1) undergoes isomerization to form vibrationally hot and rotationally cold EO in an excited electronic state, or (2) undergoes dissociation to form vibrationally and rotationally hot molecular products in excited electronic states. The electronically excited EO emits a UV photon to produce vibrationally hot and rotationally cold EO in its ground electronic state. This EO then emits its vibrational energy in the infrared (IR) and gives rise to the UIR bands. The electronically excited dissociation products also emit UV photons to produce vibrationally and rotationally hot molecules in their ground electronic states. These daughter molecules also emit in the IR and give rise to the UIR continuum. While EO and its isomers are plausible candidates for the source of the UIR spectrum, we have also found that the fundamental vibrational frequencies of cyclopropenylidene (c-C3H2) also match well with the UIR spectral bands, perhaps indicating that more than one small carbonaceous molecule (SCM) is involved.
Bernstein Lawrence
Lynch David K.
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