Knowledge Bank

Spectroscopic studies on the $Q0$ absorption bands of nickel octaethylporphyrin (NiOEP) crystals are reported and interpreted. These include polarized reflection spectra of oriented single crystals; circular polarized Zeeman, and MCD spectra of polycrystalline samples. Two Davydov or factor groupd components are assigned. The higher energy component is parity forbidden but vibronically coupled to the lower one. MCD, Zeeman and zero-field data determine the symmetry of the vibration and the value of the coupling coefficient. An estimate for the effective orbital angular momentum coupling parameter is calculated from the MCD data.