15min:

L. MARGULÈS AND R. A. MOTIYENKO, Laboratoire PhLAM, CNRS UMR 8523, Université de Lille 1, 59655 Villeneuve d'Ascq Cedex, France; AND J.-C. GUILLEMIN, Sciences Chimiques de Rennes, UMR 6226 CNRS-ENSCR, Avenue du Général Leclerc, CS 50837, 35708 Rennes Cedex 7, France.

Our studies of the isotopic species of ¹³C and D isotopologues of methyl formate (HCOOCH₃), have allowed the detection of more than 600 lines in Orion\footnoteCarvajal,~M.; Margulès,~L.; Tercero,~B.; et al. A&A ~500, (2009) 1109^,. This confirms that many observed U-lines are coming from isotopic species of one of the most abundant molecules in space. Since its first detection in 1976 in SgrB2 and in Orion A, acetaldehyde (CH₃CHO) was detected in many other numerous objects. If its deuterated species (CD₃CHO and CH₃CDO) have been previously studied in the millimeterwave range, the data concerning the ¹³C species are limited to few lines measured in 1957 up to 40 GHz. In this context we decided to study the ¹³C species of acetaldehyde. Acetaldehyde molecule displays a large amplitude motion: the hindered rotation of the methyl group with respect to the rest of the molecule. The analysis is performed with the Rho Axis Method. Recent versions of the codes include high orders term in order to reproduce the observed frequencies for large quantum numbers values as J-values as high as 70^a,b,. Measurements and analysis of the rotational spectra of ¹³C isotopic species are in progress in Lille with a solid-state submillimetre-wave spectrometer (50-950 GHz), the first results will be presented. This work is supported by the contract ANR-08-BLAN-0054 and by the Programme National de Physico-Chimie du Milieu Interstellaire (PCMI-CNRS).