2015A&A...577A..91K

The recent discovery of methyl acetate in Orion KL makes vinyl acetate, CH₃C=OOCH=CH₂, a potential molecule in the interstellar medium. We obtained very accurate spectroscopic constants in a comprehensive laboratory analysis of its rotational spectra which can be used to predict those transition frequencies towards interstellar sources. We present the experimental study and theoretical analysis of the ground torsional state of vinyl acetate in a large spectral range for astrophysical use. The room-temperature rotational spectrum of vinyl acetate has been measured from 125 to 305 GHz to provide direct frequencies to the astronomical community. Additional measurements have also been made using a broadband CP-FTMW spectrometer in the region of 6-18 GHz. Transition lines, corresponding to the most stable conformer, have been observed and assigned. All the rotational transitions revealed the A-E splitting due to the methyl internal rotation and had to be treated with a specific internal rotation code (BELGI-Cs). We analyzed 2508 transitions up to J''=75 for v_t=0 for the most stable conformer of vinyl acetate. The new lines were globally fitted with previously published data and 24 parameters of the Hamiltonian were accurately determined. The spectral features of vinyl acetate were then searched for in Orion KL. Using the whole line survey of Orion KL (80-280GHz) obtained with the IRAM 30 m radio telescope we can provide only an upper limit to the column density of vinyl acetate. However, using the ALMA science verification data we obtain a tentative detection of this species that will require further search at other frequencies to confirm its presence in this high mass star forming region.