Vibronic Interactions in the Naphthalene Molecule

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Abstract
The second singlet-singlet absorption system of naphthalene (1 B 2u) has been examined in diverse host media at low temperature. Naphthalene substituted in durene and p-xylene crystals reveals hundreds of narrow lines (w 1/2 ∼2 cm−1) within the first 1500 cm−1 of 1 B 2u, Although the same gross band contours occur in all mixed crystal systems studied, each provided unique internal structure; also each deuterium isotope of naphthalene has a unique internal line pattern. This complexity is shown to derive from resonant vibronic interference between the 1 B 2u, electronic configuration and the underlying 1 B 3u vibronic manifold. It is a clear demonstration of the detailed interactions responsible for radiationless processes in such systems. The structure admits to a direct quantitative analysis by means of extended Herzberg-Teller theory and provides coupling terms within such a framework.