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, C2v potential minima. Fluorescence quantum yield in the deuterated molecule is nearly an order of magnitude higher than in 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. 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.