TY - JOUR

T1 - Millimetre and sub-millimetre spectroscopy of doubly deuterated acetaldehyde (CHD2CHO) and first detection towards IRAS 16293-2422

AU - Asensio, J. Ferrer

AU - Spezzano, S.

AU - Coudert, L. H.

AU - Lattanzi, V.

AU - Endres, C. P.

AU - Jorgensen, J. K.

AU - Caselli, P.

PY - 2023/2/24

Y1 - 2023/2/24

N2 - Context. The abundances of deuterated molecules with respect to their main isotopologue counterparts have been determined to be orders of magnitude higher than expected from the cosmic abundance of deuterium relative to hydrogen. The increasing number of singly and multi-deuterated species detections helps us to constrain the interplay between gas-phase and solid-state chemistry and to understand better deuterium fractionation in the early stages of star formation. Acetaldehyde is one of the most abundant complex organic molecules (COMs) in star-forming regions and its singly deuterated isotopologues have already been observed towards protostars.Aims. A spectroscopic catalogue for astrophysical purposes is built for doubly deuterated acetaldehyde (CHD2CHO) from measurements in the laboratory. With this accurate catalogue, we aim to search for and detect this species in the interstellar medium and retrieve its column density and abundance.Methods. Sub-millimetre wave transitions were measured for the non-rigid doubly deuterated acetaldehyde CHD2CHO displaying hindered internal rotation of its asymmetrical CHD2 methyl group. An analysis of a dataset consisting of previously measured microwave transitions and of the newly measured ones was carried out with an effective Hamiltonian which accounts for the tunnelling of the asymmetrical methyl group.Results. A line position analysis was carried out, allowing us to reproduce 853 transition frequencies with a weighted root mean square standard deviation of 1.7, varying 40 spectroscopic constants. A spectroscopic catalogue for astrophysical purposes was built from the analysis results. Using this catalogue, we were able to detect, for the first time, CHD2CHO towards the low-mass proto-stellar system IRAS 16293-2422 utilising data from the ALMA Proto-stellar Interferometric Line Survey.Conclusions. The first detection of the CHD2CHO species allowed for the derivation of its column density with a value of 1.3x10(15) cm(-2) and an uncertainty of 10-20%. The resulting D-2/D ratio of similar to 20% is found to be coincident with D-2/D ratios derived for other COMs towards IRAS 16293-2422, pointing to a common formation environment with enhanced deuterium fractionation.

AB - Context. The abundances of deuterated molecules with respect to their main isotopologue counterparts have been determined to be orders of magnitude higher than expected from the cosmic abundance of deuterium relative to hydrogen. The increasing number of singly and multi-deuterated species detections helps us to constrain the interplay between gas-phase and solid-state chemistry and to understand better deuterium fractionation in the early stages of star formation. Acetaldehyde is one of the most abundant complex organic molecules (COMs) in star-forming regions and its singly deuterated isotopologues have already been observed towards protostars.Aims. A spectroscopic catalogue for astrophysical purposes is built for doubly deuterated acetaldehyde (CHD2CHO) from measurements in the laboratory. With this accurate catalogue, we aim to search for and detect this species in the interstellar medium and retrieve its column density and abundance.Methods. Sub-millimetre wave transitions were measured for the non-rigid doubly deuterated acetaldehyde CHD2CHO displaying hindered internal rotation of its asymmetrical CHD2 methyl group. An analysis of a dataset consisting of previously measured microwave transitions and of the newly measured ones was carried out with an effective Hamiltonian which accounts for the tunnelling of the asymmetrical methyl group.Results. A line position analysis was carried out, allowing us to reproduce 853 transition frequencies with a weighted root mean square standard deviation of 1.7, varying 40 spectroscopic constants. A spectroscopic catalogue for astrophysical purposes was built from the analysis results. Using this catalogue, we were able to detect, for the first time, CHD2CHO towards the low-mass proto-stellar system IRAS 16293-2422 utilising data from the ALMA Proto-stellar Interferometric Line Survey.Conclusions. The first detection of the CHD2CHO species allowed for the derivation of its column density with a value of 1.3x10(15) cm(-2) and an uncertainty of 10-20%. The resulting D-2/D ratio of similar to 20% is found to be coincident with D-2/D ratios derived for other COMs towards IRAS 16293-2422, pointing to a common formation environment with enhanced deuterium fractionation.

KW - ISM: molecules

KW - ISM: clouds

KW - ISM: abundances

KW - radio lines: ISM

KW - stars: formation

KW - line: identification

KW - CENTRIFUGAL-DISTORTION COEFFICIENTS

KW - COMPLEX ORGANIC-MOLECULES

KW - ASYMMETRIC-TOP MOLECULES

KW - MICROWAVE-SPECTRUM

KW - ROTATION INTERACTIONS

KW - INTERNAL-ROTATION

KW - HINDERED ROTATION

KW - ALMA OBSERVATIONS

KW - METHYL-ALCOHOL

KW - SOLID METHANOL

U2 - 10.1051/0004-6361/202245442

DO - 10.1051/0004-6361/202245442

M3 - Journal article

VL - 670

JO - Astronomy & Astrophysics

JF - Astronomy & Astrophysics

SN - 0004-6361

M1 - A177

ER -