Long-lived high-spin states of small anions:6Πstate ofCO−

Abstract

Stimulated by recent mass spectrometric observations, we have investigated several high-spin states of ${\mathrm{CO}}^{\mathrm{\ensuremath{-}}}$ to identify the observed anionic state. We follow a general construction principle for long-lived anionic states of small molecules: A possibly long-lived anionic state possesses several ``equivalent'' valence electrons bound to a positively charged ion core. Applying this idea to ${\mathrm{CO}}^{\mathrm{\ensuremath{-}}},$ we have found a ${}^{6}\ensuremath{\Pi}$ state which is stable with respect to both single-electron emission and dissociation. Since all different decay channels are spin forbidden, this state is long-lived, and will be observable in a mass spectrometer.