Low and intermediate energy electron collisions with the C−2 molecular anion

Calculations are presented which use the molecular R-matrix with pseudo-states (MRMPS) method to treat electron impact electron detachment and electronic excitation of the carbon dimer anion. Resonances are found above the ionization threshold of C[?]2 with 1S+g, 1Pg and 3Pg symmetry. These are shape resonances trapped by the effect of an attractive polarization potential competing with a repulsive Coulomb interaction. The Pg resonances are found to give structure in the detachment cross section similar to that observed experimentally. Both excitation and detachment cross sections are found to be dominated by large impact parameter collisions whose contribution is modelled using the Born approximation