Resonance line shapes in the Rydberg spectra of large molecules

Abstract

The theory of line shapes in absorption to nearly degenerate states of large molecules is re‐examined by relaxing the assumptions of the Bixon–Jortner model. The use of a single interaction strength to describe the coupling of a given sparse state to all members of the quasicontinuum of dissipative states is shown to produce an absorption intensity that vanishes at an energy determined independently of the assumed zero‐order quasicontinuum level spacings. A more general theory is developed. The variation in coupling strength to nearby quasicontinuum states is shown to yield an absorption intensity that fails to vanish near resonance, and sometimes to suppress the characteristic features of the antiresonance line shape expected on the basis of simpler models, thus accounting for the scarcity of observable antiresonances and for some features of the naphthalene absorption spectrum. A new interference effect, involving the coalescence of neighboring absorption peaks into a single narrowed peak, is demonstrated.