Excitation profiles and depolarization ratios of some prominent Raman lines in oxyhaemoglobin and ferrocytochrome c in the pre‐resonant and resonant region of the Q‐band

The depolarization ratio‐dispersion curves and the excitation profiles of oxyhaemoglobin (1375, 1583, 1638 cm−1) and ferrocytochrome c Raman lines have been measured in the pre‐resonant and resonant regions of the Q‐band, respectively. The experimental data are interpreted by fifth‐order Loudon theory of the polarizibility tensor, including symmetry lowering of the haem group and the creation and subsequent annihilation of a second phonon. The fitting constants needed to fit the experimental data are related to vibronic coupling matrix elements due to the Raman and the second phonon. They also contain distortions δQΓ, lowering the ideal D4h, symmetry of the functional haem group. These distortions can be classified due to the Raman‐allowed representations A1g, B1g, B2g and A2g in D4h symmetry. Thus, from the fitting procedure one obtains detailed information about the actual symmetry of the haem group.