Knowledge Bank

From near infrared circular dichroism and absorption studies we have identified $d\to d$ transitions of the iron in hemoproteins for the first time. Magnetic dipole allowed $d\to d$ transitions are distinguished, from e.g. weak ligand or charge transfer transitions, by their relatively larger ratio of rotational strength to dipole strength. The determination of d orbital energy differences by optical spectroscopy is most favorable for the diamagnetic ferrous hemoproteins. The Dq value for the porphyrin ring of ferrocytochrome c is $1700-1900cm-1$ in excellent agreement with extended H""{u}ckel calculations.