In a number of physical environments, electron collisions with molecules and molecular ions initiate and drive the chemistry of the system. In general due to the large mass difference between the electron and target, the cross section is dominated by resonant processes, where the electron can temporarily attach to the molecule and change the forces felt between its atoms for a period of time comparable to a vibrational period. This can lead to resonant vibrational excitation and dissociative attachment, for neutral targets, or dissociative recombination in the case of ions. We outline the basic theory that underlies these processes, and our approach to study them. We then illustrate the method with the study of dissociative recombination for the
molecular ions and dissociative attachment of C2H2.