Complex Organic Molecules in Protostars with ALMA Spectral Surveys (COMPASS) VIII. First interstellar detection of fully deuterated methyl cyanide
Abstract
Deuteration is a powerful metric to gain insight into the formation pathways of interstellar molecules in star forming regions. Our primary goal is to search for the fully deuterated form of methyl cyanide, CD3CN, in the ISM. We used a sensitive imaging spectral survey of the protostellar system L1551 IRS5 in the Taurus molecular cloud performed as part of the Large Program carried out with the Atacama Large Millimeter/submillimeter Array (ALMA) called Complex Organic Molecules in Protostars with ALMA Spectral Surveys (COMPASS). We derived the column densities of methyl cyanide and several of its less abundant isotopologs, including deuterated ones, under the assumption of local thermodynamic equilibrium. All three deuterated isotopologs of methyl cyanide were detected toward the northern binary component of L1551 IRS5. In particular, we report the first interstellar detection of CD3CN. The measured D/H ratio increases by about half an order of magnitude from one deuterated isotopolog to the next, in a similar way as what was measured for methanol in several other low-mass protostars. This suggests that methyl cyanide predominantly forms like methanol on the surface of dust grains during the cold prestellar phase. However, the measured factor of 2 difference between the D/H ratios of methyl cyanide and methanol may either indicate that gas-phase processes during the warm-up stage contribute approximately equally to the production of methyl cyanide, or that methyl cyanide and its deuterated isotopologs are formed during the prestellar phase at a somewhat earlier time than methanol. Multiply deuterated isotopologs are crucial to understand the formation and inheritance of molecules in the ISM by coupling observations and astrochemical models. Unfortunately, no model has so far investigated the deuteration of methyl cyanide up to the fully deuterated form. [Abridged]
Related
- Complex Organic Molecules in Protostars with ALMA Spectral Surveys (COMPASS) VII. First interstellar detection of fully deuterated methanol
- Complex Organic Molecules in Protostars with ALMA Spectral Surveys (COMPASS) V. Tracing cavity walls and shocked knots with nonthermally desorbed CH3OH in BHR71-IRS1
- Complex Organic Molecules in Protostars with ALMA Spectral Surveys (COMPASS)
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- Complex Organic Molecules in Protostars with ALMA Spectral Surveys (COMPASS) II. Approach to data reduction and products for line-rich broadband (sub)millimeter spectra
BibTeX
@misc{belloche2026complex,
title = {{Complex Organic Molecules in Protostars with ALMA Spectral Surveys (COMPASS) VIII. First interstellar detection of fully deuterated methyl cyanide}},
author = {A. Belloche and J. K. Jørgensen and M. N. Drozdovskaya and S. Spezzano and A. Coutens and J. -E. Lee and F. Cruz-Sáenz de Miera and D. Harsono and J. -H. Jeong and S. Maret and B. A. McGuire and P. Nazari and A. L. Plunkett and Y. -L. Yang and H. -S. Yun},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.40365},
eprint = {2610.40365},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.40365},
}
RIS
TY - UNPB
TI - Complex Organic Molecules in Protostars with ALMA Spectral Surveys (COMPASS) VIII. First interstellar detection of fully deuterated methyl cyanide
AU - A. Belloche
AU - J. K. Jørgensen
AU - M. N. Drozdovskaya
AU - S. Spezzano
AU - A. Coutens
AU - J. -E. Lee
AU - F. Cruz-Sáenz de Miera
AU - D. Harsono
AU - J. -H. Jeong
AU - S. Maret
AU - B. A. McGuire
AU - P. Nazari
AU - A. L. Plunkett
AU - Y. -L. Yang
AU - H. -S. Yun
PY - 2026
DA - 2026/10/29
PB - arXiv
DO - 10.48550/arxiv.2610.40365
UR - https://arxiv.org/abs/2610.40365
AB - Deuteration is a powerful metric to gain insight into the formation pathways of interstellar molecules in star forming regions. Our primary goal is to search for the fully deuterated form of methyl cyanide, CD3CN, in the ISM. We used a sensitive imaging spectral survey of the protostellar system L1551 IRS5 in the Taurus molecular cloud performed as part of the Large Program carried out with the Atacama Large Millimeter/submillimeter Array (ALMA) called Complex Organic Molecules in Protostars with ALMA Spectral Surveys (COMPASS). We derived the column densities of methyl cyanide and several of its less abundant isotopologs, including deuterated ones, under the assumption of local thermodynamic equilibrium. All three deuterated isotopologs of methyl cyanide were detected toward the northern binary component of L1551 IRS5. In particular, we report the first interstellar detection of CD3CN. The measured D/H ratio increases by about half an order of magnitude from one deuterated isotopolog to the next, in a similar way as what was measured for methanol in several other low-mass protostars. This suggests that methyl cyanide predominantly forms like methanol on the surface of dust grains during the cold prestellar phase. However, the measured factor of 2 difference between the D/H ratios of methyl cyanide and methanol may either indicate that gas-phase processes during the warm-up stage contribute approximately equally to the production of methyl cyanide, or that methyl cyanide and its deuterated isotopologs are formed during the prestellar phase at a somewhat earlier time than methanol. Multiply deuterated isotopologs are crucial to understand the formation and inheritance of molecules in the ISM by coupling observations and astrochemical models. Unfortunately, no model has so far investigated the deuteration of methyl cyanide up to the fully deuterated form. [Abridged]
ER -