Investigation of the rotational spectrum of CD${}_3$OD and an astronomical search toward IRAS 16293$-$2422

Abstract

Solar-type prestellar cores and protostars display large amounts of deuterated organic molecules. Recent findings on CHD${}_2$OH and CD${}_3$OH toward IRAS 16293-2422 suggest that even fully deuterated methanol, CD${}_3$OD, may be detectable as well. However, searches for CD${}_3$OD are hampered in particular by the lack of intensity information from a spectroscopic model. The objective of the present investigation is to develop a spectroscopic model of CD${}_3$OD in low-lying torsional states that is sufficiently accurate to facilitate searches for this isotopolog in space. We carried out a new measurement campaign for CD${}_3$OD involving two spectroscopic laboratories that covers the 34 GHz-1.1 THz range. A torsion-rotation Hamiltonian model based on the rho-axis method was employed for our analysis. Our resulting model describes the ground and first excited torsional states of CD${}_3$OD well up to quantum numbers $J\le 51$ and $K_a\le 23$. We derived a line list for radio-astronomical observations from this model that is accurate up to at least 1.1 THz and should be sufficient for all types of radio-astronomical searches for this methanol isotopolog. This line list was used to search for CD${}_3$OD in data from the Protostellar Interferometric Line Survey of IRAS 16293$-$2422 obtained with the Atacama Large Millimeter/submillimeter Array. While we found several emission features that can be attributed largely to CD${}_3$OD, their number is still not sufficiently high enough to establish a clear detection. Nevertheless, the estimate of 2$\times 10^{15}$ cm${}^{-2}$ derived for the CD${}_3$OD column density may be viewed as an upper limit that can be compared to column densities of CD${}_3$OH, CH${}_3$OD, and CH${}_3$OH. The comparison indicates that the CD${}_3$OD column density toward IRAS 16293-2422 is in line with the enhanced D/H ratios observed for multiply deuterated complex organic molecules.

10 pages total, including figures, tables, and references; abstract slightly shortened; Astron. Astrophys., accepted

References in corpus (7)

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