Excess energy dependence of radiationless transitions in naphthalene vapor: Competition between internal conversion and intersystem crossing

Experimental and theoretical evidence for effective internal conversion to the ground state from highly vibrationally excited states is presented for naphthalene-h₈ and -d₈. The evidence is based upon both the variation of the deuteron effect and strong exponential increase of the nonradiative decay rate as observed in the excess energy region between 10 000 and 18 000 cm^-1. The calculations are only consistent with the experiments if it is assumed that the excess energy does not redistribute completely according to the statistical weighting among the normal modes but rather stays in the class of strongly accepting modes.