  We report the first detection in interstellar space of the 3-cyano propargyl
radical (CH2C3N). This species was observed in the cold dark cloud TMC-1 using
the Yebes 40m telescope. A total of seven rotational transitions for both
ortho- and para-CH2C3N species were observed in the 31.0-50.4 GHz range. We
derive a total column density of (1.6 +/- 0.4)e11 cm-2 and an ortho/para ratio
of 2.4 +/- 1.2, which implies an abundance ratio CH2C3N/CH3C3N around 0.1, in
sharp contrast with the smaller analogues, in which case CH2CN/CH3CN = 3. This
indicates that the chemistry of the cyanides CH2C3N and CH3C3N behaves
differently to that of the smaller analogues CH2CN and CH3CN. According to our
chemical model calculations, the radical CH2C3N is mostly formed through the
neutral-neutral reactions C + CH2CHCN, C2 + CH3CN, and CN + CH2CCH together
with the dissociative recombination of the CH3C3NH+ ion with electrons. The
neutral-neutral reaction N + C4H3 could also lead to CH2C3N, although its role
is highly uncertain. The identified radical CH2C3N could play a role in the
synthesis of large organic N-bearing molecules, such as benzonitrile (c-C6H5CN)
or nitrogen heterocycles.
