Energy dependence of radiationless relaxation in methylglyoxal

Measurements are reported for the biexponential decay parameters as a function of excitation energy for luminescence from the lowest energy excited singlet state (S₁) of methylglyoxal. The results are interpreted in terms of a kinetic scheme incorporating reversible decay between S₁ and a set of isoenergetic accepting levels. Correspondence with a quantum mechanical model yields coupling matrix elements and densities of accepting levels. Some fundamental decay rate constants for S₁ in glyoxal, methylglyoxal, and in biacetyl are found to be strikingly similar. This similarity may be explained with a simple theoretical scheme.