Energy States and Intermolecular Interactions in Molecular Aggregates: Resonance Pair Spectra of Crystalline Naphthalene

Abstract

Very high‐resolution optical spectra reveal fine structure in the 1 B 2u → 1 A g and 3 B 1u → 1 A g electronic transitions of naphthalene isotopic mixed crystals, C10H8 as a guest in a C10D8 host. Extensive experimental data allow the spectral lines to be characterized and assigned. Some of the structure corresponds to the resonance splitting arising from neighboring pairs of guest molecules in the host lattice. In the Frenkel tight‐binding approximation, this structure gives directly the intermolecular excitation transfer matrix elements responsible for the exciton mobilities and the energy band structures of both pure and mixed molecular crystals. For the 1 B 2u state the largest interchange equivalent interactions are approximately + 15.3 cm−1 and + 3 cm−1 while the largest translation equivalent interactions are approximately + 3.7, − 5.1, − 7.9, and − 3.3 cm−1. For the 3 B 1u state the largest interchange equivalent interaction is 1.25 cm−1.