Large molecule relaxation: Spectroscopy, structure, and vibrational energy redistribution in naphthazarin

Analysis of IR and laser induced fluorescence spectra of naphthazarin in rare gas matrices shows clearly that its vibrational potential is characterized by well localized, deep, C_2v potential minima. Fluorescence quantum yield in the deuterated molecule is nearly an order of magnitude higher than the H₂ and HD isotopic species. Vibrational relaxation in the upper state is remarkably slow and intense unrelaxed emission from a large number of excited vibrational levels is observed. Studies of the unrelaxed emission provide insight into the vibrational relaxation process. Vibrational energy redistribution clearly proceeds via specific pathways and not in a random, statistical manner. The relaxation rates and pathways exhibit only a mild dependence upon temperature and upon the matrix medium.