Generalized Susceptibility Theory. IV. The Structure of Electronic Absorption Spectra of Linear Polymers

Abstract

The role of the monomerabsorptionspectrum in determining the absorptionspectrum of a linear polymer is studied in terms of a linear response theory formulation of the complex, frequency‐dependent polarizability of the polymer. It is pointed out that a Ketteler‐Helmholtz dispersion (combination of positive and negative frequency Lorentzians) is a fundamental form in the theory and, accordingly, modelabsorption spectra for the monomer, consisting of sets of Ketteler‐Helmholtz bands, are used. In each case the polymerspectrum is calculated for various intermolecular coupling strengths. Under the right conditions, all of the intensity from a set of monomer bands appears in a single collective mode of the polymer [cf. A. Herzenberg and A. Modinos, Proc. Phys. Soc. (London) 87, 597 (1966)]. The spectral requirements for such strong coupling and the spectral features of the collective mode are determined. The latter is observed to become a Ketteler‐Helmholtz in the strong coupling limit. The contribution of monomer transitions outside the observed frequency range is also considered.