  For decades astronomers and astrophysicists believed that only positively
charged ions were worthy of relevance in drawing the networks for possible
chemical reactions in the interstellar medium, as well as in modeling the
physical conditions in most of astrophysical environments. Thus, molecular
negative ions received minor attention until their possible existence was
observationally confirmed (discovery of the first interstellar anion, C6H-),
about thirty years after the first physically reasonable proposal on their
actual detection was theoretically surmised by E.Herbst. In an astrophysical
context, their role should be then found in their involvement in the charge
balance as well as in the chemical evolution of the considered environment:
depending on their amount and on the global gas density, in fact, the possible
evolutive scenario could be susceptible of marked variations on the estimated
time needed for reaching the steady state, their presence having thus also
important repercussions on the final chemical composition of a given
environment. The main reasons that originally motivated us to undertake the
present work, were at least two. First of all, we intended to demonstrate the
importance of resonances in forming molecular anions in different astrophysical
environments. Secondly, we were attracted by the possibility of investigating
the occurrence of radiationless paths like intramolecular vibrational
redistributions to account for the dissipation of the extra energy initially
carried by the impinging electron. Accordingly, the present PhD represents a
theoretical/computational work which deals with an area placed at the boundary
between (molecular) astrophysics, quantum collision thery, and theoretical
chemistry. The three molecular species whose behaviour under low-energy
electron collisions will be discussed are: the ortho-benzyne, the coronene and
the carbon nitride.
