  The formation of anionic species in the interstellar medium from interaction
of linear molecules containing carbon, nitrogen and hydrogen as atomic
components (polyynes) with free electrons in the environment is modelled via a
quantum treatment of the collision dynamics. The ensuing integral cross
sections are employed to obtain the corresponding attachment rates over a broad
range of temperatures for the electrons. The calculations unequivocally show
that a parametrization form often employed for such rates yields a broad range
of values that turn out to be specific for each molecular species considered,
thus excluding using a unique set for the whole class of polyynes.
