High-excitation lines of deuterated formaldehyde (HDCO) in the Orion molecular cloud

Journal Article · Sat Dec 14 23:00:00 EST 1985 · Astrophys. J.; (United States)

DOI:https://doi.org/10.1086/163761· OSTI ID:5881204

Loren, R B; Wootten, A

Five HDCO lines (up to 35 cm/sup -1/) have been detected in the narrow OMC-1 kinematic component. The best estimate of the (HDCO)/(H/sub 2/CO) abundance ratio in OMC-1 is 0.01-0.03, at least an order of magnitude greater than the observed (DCO/sup +/)/(HCO/sup +/) abundance ratio. The (DCO/sup +/)/(HCO/sup +/) ratio greatly exceeds the (HDCO)/(H/sub 2/CO) radio in cold clouds where the enhancement of both HDCO and DCO/sup +/ abundances originates from H/sub 2/D/sup +/. H/sub 2/D/sup +/ is abundant only at temperatures lower than found in OMC-1. The combination of a low (DCO/sup +/)/(HCO/sup +/) and high (HDCO)/(H/sub 2/CO) 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 CH/sub 3//sup +/ is greater than for the HD+H/sub 3//sup +/ reaction. The CH/sub 2/D/sup +/ thus formed survives to higher temperatures than H/sub 2/D/sup +/. Subsequent reactions with H/sub 2/ lead to CH/sub 4/D/sup +/ which by electronic recombination forms CH/sub 2/D. The HDCO (H/sub 2/CO) forms in the neutral-neutral reaction of CH/sub 2/D (CH/sub 3/) and O. These reactions are not competitive in forming a variety of deuterated molecules at low temperatures since electronic recombination rapidly removes CH/sub 2/D/sup +/ and CH/sub 4/D/sup +/ ions while the abundant H/sub 2/D/sup +/ ion is slow to recombine, as reported by Smith and Adam in 1984.

• Research Organization: Millimeter Wave Observatory, Electrical Engineering Research Laboratory, and Department of Astronomy, The University of Texas at Austin
• OSTI ID: 5881204
• Journal Information: Astrophys. J.; (United States), Journal Name: Astrophys. J.; (United States) Vol. 299:2; ISSN ASJOA
• Country of Publication: United States
• Language: English

Related Subjects

640105* -- Astrophysics & Cosmology-- Galaxies
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ABUNDANCE
ALDEHYDES
CHARGED PARTICLES
CHEMICAL REACTIONS
DEUTERATION
ENERGY LEVELS
ENERGY-LEVEL TRANSITIONS
FORMALDEHYDE
HYDROCARBONS
INTERSTELLAR GRAINS
ION EXCHANGE
IONS
ISOTOPE RATIO
NEBULAE
ORGANIC COMPOUNDS
PARTICLES
RECOMBINATION
SPECTRA