Reassignment of the AlSi— photoelectron spectrum by ab initio configuration interaction calculations

Complete active space self-consistent field (CASSCF) and multi-reference singles and doubles configuration interaction (MRSDCI) theoretical calculations of the energy and wavefunctions for the low lying states of AlSi— and AlSi with various internuclear distances are used to interpret the recently reported experimental photoelectron spectrum of AlSi—. On the basis of the MRSDCI calculations it is found that the lowest 3II and 3Σ— states of AlSi— lie very close in energy to one another, with the 3Σ— state being the more stable. The ground state of AlSi is determined to be 4Σ—. In terms of peak positions and intensities, semiquantitative agreement is observed between the experimental and the theoretically derived spectra. New assignments have been made for some of the previously assigned photoelectron peaks on the basis of these MRSDCI results.