Other
Scientific paper
Dec 1985
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1985apj...299..947l&link_type=abstract
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 299, Dec. 15, 1985, p. 947-955. Research supported by the California Instit
Other
18
Astronomical Spectroscopy, Deuterium Compounds, Formaldehyde, Interstellar Matter, Molecular Clouds, Orion Nebula, Abundance, Interstellar Chemistry, Ionic Reactions, Line Spectra
Scientific paper
Five HDCO lines (up to 35 cm-1) have been detected in the narrow OMC-1 kinematic component. The best estimate of the [HDCO]/[H2CO] abundance ratio in OMC-1 is 0.01-0.03, at least an order of magnitude greater than the observed [DCO+]/[HCO+] abundance ratio. The [DCO+]/[HCO+] ratio greatly exceeds the [HDCO]/[H2CO] ratio in cold clouds where the enhancement of both HDCO and DCO+ abundances originates from H2D+. H2D+ is abundant only at temperatures lower than found in OMC- 1. The combination of a low [DCO+]/[HCO+] and high [HDCO]/[H2CO] abundance ratio in OMC-1 requires a different HDCO formation route at high temperature. This alternate HDCO formation path can occur because the exothermicity of the ion exchange reaction of HD and CH3+ is greater than for the HD + H3+ reaction. The CH2D+ thus formed survives to higher temperatures than H2D+. Subsequent reactions with H2 lead to CH4D+ which by electronic recombination forms CH2D. The HDCO (H2CO) forms in the neutral-neutral reaction of CH2D (CH3) and O. These reactions are not competitive in forming a variety of deuterated molecules at low temperatures since electronic recombination rapidly removes CH2D+ and CH4D+ ions while the abundant H2D+ ion is slow to recombine, as reported by Smith and Adam in 1984.
Loren Robert B.
Wootten Al
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