Abstract
Context. Detection of deuterated species may provide information on the evolving chemistry in the earliest phases of star-forming regions. For molecules with two isomeric forms of the same isotopic variant, gas-phase and solid-state formation pathways can be differentiated using their abundance ratio. Aims. Spectroscopic databases for astrophysical purposes are built for the two mono deuterated isomeric species CH2DCOH and CH3COD of the complex organic molecule acetaldehyde. These databases can be used to search and detect these two species in astrophysical surveys, retrieving their column density and therefore abundances. Methods. Submillimeter wave and terahertz transitions were measured for mono deuterated acetaldehyde CH2DCOH which is a non-rigid species displaying internal rotation of its asymmetrical CH2D methyl group. An analysis of a dataset consisting of previously measured microwave data and the newly measured transition was carried out with a model accounting for the large amplitude torsion. Results. The frequencies of 2556 transitions are reproduced with a unitless standard deviation of 2.3 yielding various spectroscopic constants. Spectroscopic databases for astrophysical purposes were built for CH2DCOH using the results of the present analysis and for CH3COD using the results of a previous spectroscopic investigation. These two species were both searched for and are detected toward a low-mass star-forming region. Conclusions. We report the first detection of CH2DCOH (93 transitions) and the detection of CH3COD (43 transitions) species in source B of the IRAS 16293−2422 young stellar binary system located in the ρ Ophiuchus cloud region, using the publicly available ALMA Protostellar Interferometric Line Survey.
Highlights
Acetaldehyde and its isotopic species have been the subject of many spectroscopic investigations, due to their astrophysical relevance and to the large amplitude nature of the internal rotation of the methyl group
Spectroscopic databases for astrophysical purposes are built for the two mono deuterated isomeric species CH2DCOH and CH3COD of the complex organic molecule acetaldehyde
Submillimeter wave and terahertz transitions were measured for mono deuterated acetaldehyde CH2DCOH which is a nonrigid species displaying internal rotation of its asymmetrical CH2D methyl group
Summary
Acetaldehyde and its isotopic species have been the subject of many spectroscopic investigations, due to their astrophysical relevance and to the large amplitude nature of the internal rotation of the methyl group. For complex organic molecules (organic molecules containing at least six atoms, Herbst & van Dishoeck 2009), there usually exist two different isomeric mono deuterated species and their abundance ratio yields additional information about interstellar chemistry. This may allow differentiation of gas-phase and grain surface formation pathways. We first spectroscopically characterized the species that has a partially deuterated CH2D methyl group, prior to designing its database.
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