In the [Mn(HO)] metal complex, manganese has an oxidation state of +2, thus it is a d ion. HO is a weak field ligand (spectrum shown below), and according to the Tanabe–Sugano diagram for d ions, the ground state is A.  Note that there is no sextet spin multiplicity in any excited state, hence the transitions from this ground state are expected to be spin-forbidden and the band intensities should be low. From the spectra, only very low intensity bands are observed (low molar absorptivity (ε) values on y-axis).