Rotational spectroscopy of isotopic vinyl cyanide, H$_2$C=CH$-$C$\equiv$N, in the laboratory and in space

TL;DR

This study combines laboratory rotational spectroscopy and astronomical observations to identify and analyze isotopic vinyl cyanide in space, providing improved spectroscopic data and insights into the chemical environment of interstellar hot cores.

Contribution

The paper presents the first detection of $^{13}$C isotopic vinyl cyanide in space and improves spectroscopic parameters for the main isotopic species through laboratory measurements.

Findings

$^{13}$C vinyl cyanide detected in two hot cores of Sagittarius B2(N).

Derived $^{12}$C/$^{13}$C ratio of 21 in the observed region.

Identified different evolutionary stages of the hot cores based on isotopic analysis.

Abstract

The rotational spectra of singly substituted $^{13}$C and $^{15}$N 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 $^{13}$C 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 $^{13}$C species are detected in two compact ($\sim 2.3''$), hot (170 K) cores with a column density of $\sim 3.8 \times 10^{16}$ and $1.1 \times 10^{16}$ cm$^{-2}$, respectively. In the main source, the so-called ``Large Molecule Heimat'', we derive an abundance of $2.9 \times 10^{-9}$ for each $^{13}$C species relative to H$_2$. An isotopic ratio $^{12}$C/$^{13}$C of 21 has been measured. Based on a comparison to the column densities measured for the $^{13}$C 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.