Singlet–Triplet Absorption of Crystalline Naphthalene by High-Resolution Photoexcitation Spectroscopy

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Abstract
The high-resolution singlet–triplet absorption spectrum of crystalline naphthalene at 4.2°K was obtained by a photoexcitation technique. The spectrum is presented and analyzed. The spectrum primarily consists of strong Ag modes that exhibit factor-group splitting and that are primarily polarized normal to the molecular plane. The total factor-group splitting of − 32 cm−1 is in agreement with that measured directly in absorption. The crystal polarization properties of the spectrum serve to identify the high-energy components of the Davydov pairs as belonging to the (+) or Au factor-group component. The spectrum clearly reveals the presence of certain antisymmetric modes, which appear with an intensity that is about two orders of magnitude less than that of the 0, 0.