P. Geissinger et al., TRANSITION FREQUENCY AND INTERNAL ELECTRIC-FIELD FOR PROTOPORPHYRIN-IX IN MYOGLOBIN, Molecular crystals and liquid crystals science and technology. Section A, Molecular crystals and liquid crystals, 283, 1996, pp. 249-254
The internal electric field acting on a guest molecule can be determin
ed by measuring the effect of an external electric field on the profil
e of a photochemical hole. For protoporphyrin-IX in myoglobin we obser
ve a systematic dependence of internal electric field on frequency in
the inhomogeneously broadened Q(k) band.