On the ground state of MnCO−

The ground state of MnCO− is predicted to be 5λ, which is derived from a mixture of the 3d64s2 and 3d54s24p1 occupations of Mn−. The 7λ state, which is derived from the 3d54s24p1 occupation, is found to be only slightly higher in energy. On the basis of the calculations, the two MnCO states observed in photoelectron detachment experiment are assigned as 4λ and 6λ. The computed geometries and vibrational frequencies are in reasonable agreement with experiment.