Electronic relaxation in naphthalene vapor

Fluorescence of naphthalene vapor a(1) 0.1 mm and room temperature has been studied as a function of vibrational level and excitation energy. It is shown that the quantum yield of fluorescence from different vibrational levels of the lowest excited singlet state (S-1) shows a large variation. with the emission from a big level' showing particularly high yield. The quantum yield of the emission from several virbational levels (a b(1g) level in particular) of S-1 is greater for naphthalene-h(8) than for naphthalene-d(8), contrasting the normal deuterium isotope effect on radiationless transitions. It also shown that the quantum yield of fluorescence decrease rather smoothly with increasing excitation energy in the spectral region covering the second and third absorption bands. In the same spectral region, the fluorescence quantum yield of d(8) is greater than that of h(8), and the ratio of the two yields increases smoothly with increasing energy of excitation.