Dissociative Electron Attachment to the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mrow> <mml:msub> <mml:mrow> <mml:mi>HNC</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>3</mml:mn> </mml:mrow> </mml:msub> </mml:mrow> </m

Dissociative electron attachment (DEA) to HNC_{3} is modeled theoretically using a first-principles approach. In HNC_{3}+e^{-} collisions, there is a low-energy resonance, which has a repulsive character along the H+NC_{3} coordinate and becomes a bound electronic state of the HNC_{3}^{-} anion near the equilibrium of HNC_{3}. The anion state dissociates without a potential barrier toward C_{3} N^{-}+H. The cross section and the rate coefficient of the process are computed. The obtained rate coefficient at low temperatures is 5×10^{-9} cm^{3}/s at 300 K. Such a value of the DEA rate coefficient makes the DEA process three orders of magnitude more efficient at producing negative molecular ions in interstellar space than radiative electron attachment (REA). It is suggested that negative molecular carbon-chain ions, observed in the interstellar medium, are produced by DEA rather than REA.