Vibronic coupling and a magnetic-field-induced avoided crossing in the S₁←S₀ absorption spectrum of palladiumporphin

Abstract

An avoided crossing of the 786 and 815 cm^-1 vibronic bands in the absorption spectra of palladiumporphin (PdP) in n-alkane hosts in the presence of an external magnetic field is reported. A description of this effect is presented in terms of the Zeeman perturbation and intramolecular vibronic coupling. It appears to be closely connected with the orbital degeneracy of the first excited singlet state of the free PdP molecule. It is concluded that the anticrossing is due to a bilinear term in the nuclear potential energy, which gives rise to a vibronic matrix element of 4·8 cm^-1.