Resonance Raman spectra of octaethylporphyrinato-Ni(II) and m e s o-deuterated and 15N substituted derivatives. II. A normal coordinate analysis

Abstract

Normal coordinate calculations are carried out for all the in‐plane modes of octaethylporphyrinato‐Ni (II) and its meso‐deuterated and ¹⁵N substituted derivatives. With 37 constants of a modified Urey–Bradley force field and a structural model with D_4h symmetry, 59 resonance Raman lines (A_1g+B_1g +A_2g+B_2g) and 38 infrared bands (E_u) of these three molecules are assigned. The vibrational modes of the Raman active species are represented in terms of the Cartesian atomic displacement vectors. Based on the present results, some important resonance Raman lines of hemoproteins are interpreted. The so‐called ’’oxidation state maker’’ (Band IV) is due to an in‐phase breathing‐like mode of four pyrrole rings although being somewhat deformed by the large contribution of the C_α–N symmetric stretching term. The spin state sensitive Raman lines, namely, Band I and III, are associated mainly with methine bridge (C_α–C_m) stretching modes. Two prominent anomalously‐polarized Raman lines of hemoproteins around 1580 and 1300 cm⁻¹ are primarily due to the C_α–C_m stretching and C_m–H bending modes, respectively.