Inverse deuterium isotope effect on radiationless electronic transitions

Fluorescence quantum yields, Y, front photoselected vibrational states in the S₁ manifold of anthracene and of perdeuterated anthracene in planar supersonic jets reveal a large inverse deuterium isotope effect on the non-radiative relaxation from the S₁ origin (Y_H/Y_D = 5), while for high (1500 cm⁻¹) excess energies above the S₁ origin the inverse isotope effect is eroded (Y_H/Y_D ≈ 1). Novel information emerges on intermediating states involved in intersystem crossing.