First detection of triply-deuterated methanol

¹ CESR CNRS-UPS, BP 4346, 31028 Toulouse Cedex 04, France
² Observatoire de Bordeaux, BP 89, 33270 Floirac, France
³ Department of Physics, The Ohio State University, 174 W. 18th Ave. Columbus, OH 43210-1106, USA
⁴ Laboratoire d'Astrophysique, Observatoire de Grenoble, BP 53, 38041 Grenoble Cedex 09, France
⁵ Dakota State University, 820 N. Washington Ave., Madison, SD 57042, USA
⁶ SRON, PO Box 800, 9700 AV Groningen, The Netherlands

Corresponding author: B. Parise, Berengere.Parise@cesr.fr

Received: 7 August 2003
Accepted: 3 November 2003

Abstract

We report the first detection of triply-deuterated methanol, with 12 observed transitions, towards the low-mass protostar IRAS 16293-2422, as well as multifrequency observations of ¹³CH₃OH, used to derive the column density of the main isotopomer CH₃OH. The derived fractionation ratio [ CD₃OH] /[ CH₃OH] averaged on a 10'' beam is 1.4%. Together with previous CH₂DOH and CHD₂OH observations, the present CD₃OH observations are consistent with a formation of methanol on grain surfaces, if the atomic D/H ratio is 0.1 to 0.3 in the accreting gas. Such a high atomic ratio can be reached in the framework of gas-phase chemical models including all deuterated isotopomers of H.