TERAHERTZ SPECTROSCOPY OF DEUTERATED ACETALDEHYDE: CH2DCHO

This study follows our recent investigations about deuterated methyl-top species of complex organic molecules: methanol,a methyl formate,b and dimethyl ether.c In particular these works led the first ISM detection of HCOOCH2D and CH2DOCH3. Acetaldehyde is not very abundant in the ISM, but this is a very interesting case from the spectroscopic point of view as it is an intermediate case between methyl formate and methanol. In the normal species of acetaldehyde, the barrier to internal rotationd V3 is 408cm−1 which is close to the value in methyl formatee: 373 cm−1. However, the value of the Coriolis coupling constant ρ is 0.33 in acetaldehyde which is a much larger value than in methyl formate, 0.08, meaning that the coupling between the torsion and the overall rotation is more important. The sample was not a commercial one and half of its amount is the normal species which leads to a more difficult line assignment. The spectra were recorded in Lille between 75 and 950 GHz with a solid-state submillimeter-wave spectrometer. The starting point of the analysis was the centimeter-wave measurements carried out for the sym and asymconformers.f A comparison between the approach developed for deuterated methyl formate (HCOOCH2D), based on the water dimer formalism, and that designed recently for deuterated methanol (CH2DOH) will be presented. This work is supported by the CNES and the Action sur Projets de l’INSU, PCMI.