The lowest electronic states of1Sgr;+,3Sgr;+,1Pgr;, and3Pgr; symmetry in the cyanide anion are calculated at the multiconfiguration selfhyphen;consistent field (MCSCF) level using simple pointhyphen;charge models to simulate the ionic environment in the cubic alkali halide crystals. The electrostatic potential of the lattice is essential to stabilize the excited states against autodetachment, yet the resulting spectroscopic properties are remarkably insensitive to gross changes in the lattice, including deletion of all but the six nearesthyphen;neighbor cations. The lowest excited statemdash;the state responsible for an observed UV emission spectrum of CNminus;in some alkali halidesmdash;is shown to be3Sgr;+, as in the isoelectronic N2and NO+molecules, rather than3Pgr;, as in CO. The properties of the ground electronic state are further examined at the SCF level in clusters of six alkali ions. The cations produce a lsquo;lsquo; compressionrsquo;rsquo; of the anion, decreasing the internuclear distance and increasing the vibrational frequency from the pointhyphen;charge results and thus yielding better agreement with experiment. Attempts to determine the orientational potential of the ground state of CNminus;in the lattices remain inconclusive, due to basis set limitations; however there are strong indications that in the lang;100rang; orientation favored by CNminus;in the sodium halides, the anion prefers an offhyphen;center location with the Nandash;N distance appreciably shorter than the Nandash;C distance. An examination of methods used to extract spectroscopic constants from pointwise tabulated potentials indicates that fits to closedhyphen;form potentials are better than fits to polynomials in (Rhyphen;Re) and to methods which entail numerical solution of the vibrational wave equation for the tabulated potential.
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