Rotational spectroscopy of isotopic vinyl cyanide , H 2 C = CH − C ≡ N , in the laboratory and in space ⋆

The rotational spectra of singly substituted 13C and 15N isotopic species of vinyl cyanide have been studied in natural abundances between 64 and 351 GHz. In combination with previous results, greatly improved spectroscopic parameters have been obtained which in turn helped to identify transitions of the 13C species for the first time in space through a molecular line survey of the extremely line-rich interstellar source Sagittarius B2(N) in the 3 mm region with some additional observations at 2 mm. The 13C species are detected in two compact (∼ 2.3), hot (170 K) cores with a column density of ∼ 3.8 × 1016 and 1.1 × 1016 cm−2, respectively. In the main source, the so-called “Large Molecule Heimat”, we derive an abundance of 2.9 × 10−9 for each 13C species relative to H2. An isotopic ratio 12C/13C of 21 has been measured. Based on a comparison to the column densities measured for the 13C species of ethyl cyanide also detected in this survey, it is suggested that the two hot cores of Sgr B2(N) are in different evolutionary stages. Supplementary laboratory data for the main isotopic species recorded between 92 and 342 GHz permitted an improvement of its spectroscopic parameters as well.