Low-lying electronic states of CSi^- and electron affinity of CSi according to ab initio MRD-CI calculations

Large scale MRD-CI calculations including highly excited configurations have been carried out in several large AO basis sets to determine the electronic structure of the CSi^- ion. Only two bound states are found (² Sigma ⁺ and ² Pi ), in contrast to the results for isovalent C₂^-, in which a third such species (² Sigma _u⁺) is also known. Results for the separated atomic species C, C^-, Si and Si^- employing the same theoretical method indicate that the energy separations between such negative ion states can be obtained to an accuracy of 0.1-0.2 eV. The present calculated electron affinity for CSi of 1.98 eV is thought to be of this accuracy, and it is therefore suggested that a previous estimate for this quantity of 4 eV based on indirect experimental evidence must be reconsidered.