  Neutron scattering is used to investigate the single-ion spin and orbital
excitations below the Mott-Hubbard gap in CoO. Three excitations are reported
at 0.870 $\pm$ 0.009 eV, 1.84 $\pm$ 0.03, and 2.30 $\pm$ 0.15 eV. These were
parameterized within a weak crystal field scheme with an intra-orbital exchange
of $J(dd)$=1.3 $\pm$ 0.2 eV and a crystal field splitting 10Dq=0.94 $\pm$ 0.10
eV. A reduced spin-orbit coupling of \lambda=-0.016 $\pm$ 0.003 eV is derived
from dilute samples of Mg$_{0.97}$Co$_{0.03}$O, measured to remove
complications due to spin exchange and structural distortion parameters which
split the cubic phase degeneracy of the orbital excitations complicating the
inelastic spectrum. The 1.84 eV, while reported using resonant x-ray and
optical techniques, was absent or weak for non resonant x-ray experiments and
overlaps with the expected position of a $^{4}A_{2}$ level. This transition is
absent in the dipolar approximation but expected to have a finite quadrupolar
matrix element that can be observed with neutron scattering techniques at
larger momentum transfers. Our results agree with a crystal field analysis (in
terms of Racah parameters and Tanabe-Sugano diagrams) and with previous
calculations performed using local-density band theory for Mott insulating
transition metal oxides. The results also demonstrate the use of neutron
scattering for measuring dipole forbidden transitions in transition metal oxide
systems.
