Probing the chemical complexity of amines in the ISM: detection of
  vinylamine (C$_2$H$_3$NH$_2$) and tentative detection of ethylamine
  (C$_2$H$_5$NH$_2$)
  Amines, in particular primary amines (R-NH$_2$) are closely related to the
primordial synthesis of amino acids since they share the same structural
backbone. However, only limited number of amines has been identified in the ISM
which prevents us from studying their chemistry as well as their relation to
pre-biotic species that could lead to the emergence of life. In this letter, we
report the first interstellar detection of vinylamine (C$_2$H$_3$NH$_2$) and
tentative detection of ethylamine (C$_2$H$_5$NH$_2$) towards the Galactic
Centre cloud G+0.693-0.027. The derived abundance with respect to H$_2$ is
(3.3$\pm$0.4)$\times$10$^{-10}$ and (1.9$\pm$0.5)$\times$10$^{-10}$,
respectively. The inferred abundance ratios of C$_2$H$_3$NH$_2$ and
C$_2$H$_5$NH$_2$ with respect to methylamine (CH$_3$NH$_2$) are $\sim$0.02 and
$\sim$0.008 respectively. The derived abundance of C$_2$H$_3$NH$_2$,
C$_2$H$_5$NH$_2$ and several other NH$_2$-bearing species are compared to those
obtained towards high-mass and low-mass star-forming regions. Based on recent
chemical and laboratory studies, possible chemical routes for the interstellar
synthesis of C$_2$H$_3$NH$_2$ and C$_2$H$_5$NH$_2$ are discussed.
