THZ SPECTROSCOPY OF $^{13}$C ISOTOPIC SPECIES OF A "WEED": ACETALDEHYDE

Abstract

Our studies of the isotopic species of $^{13}$C and D isotopologues of methyl formate (HCOOCH$_3$), have allowed the detection of more than 600 lines in Orion~{\bf500}, (2009) 1109}$^,$~{\bf714}, (2010) 1120}. 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 (CH$_3$CHO) was detected in many other numerous objects,~{\bf560}, (2001) 792}. If its deuterated species (CD$_3$CHO~{\bf197}, (1999) 275} and CH$_3$CDO~{\bf263}, (2010) 145}) have been previously studied in the millimeterwave range, the data concerning the $^{13}$C species are limited to few lines measured in 1957 up to 40 GHz~{\bf26}, (1957) 1695}. In this context we decided to study the $^{13}$C 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~{\bf260}, (2010) 1}. 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$^{a,b,}$~{\bf255}, (2009) 32}. Measurements and analysis of the rotational spectra of $^{13}$C isotopic species are in progress in Lille with a solid-state submillimetre-wave spectrometer (50-950 GHz), the first results will be presented.