Excited States of the Naphthalene Molecule. I. Symmetry Properties of the First Two Excited Singlet States

Abstract

The detailed polarization properties of the bands in absorption and fluorescence spectra of the naphthalene molecule have been determined by a method which makes use of a substitutional solid solution of naphthalene in durene. A single crystal of about 0.1 percent naphthalene in durene was cut so that the short axes of the naphthalenes lie strictly parallel to the surface and in one direction. The spectra were then determined in polarized light at 20°K under moderately high dispersion. The results clearly indicate that the first state is 1B3u (the transition from the ground state is long-axis polarized) and the second 1B2u. Vibrational-electronic interaction involving b1g vibrations apparently couples the first state with the second, and this results in a large short-axis polarized transition moment. This fact has been at the root of most of the previous difficulties with analysis of the spectra.