Radiationless decay from triplet state biacetyl molecules with selected vibrational energies

We report measurements of the intensity and decay rate of phosphorescence from biacetyl vapor excited into the 1Au1 electronic state as a function of additive pressure and excitation wavelength. The loss in phosphorescence intensity at short wavelengths and low additive pressure is interpreted in terms of an efficient 3AuI ↝ 1AgI intersystem crossing. The rate constant for this process has been determined as a function of excess vibrational energy in the 3 AuI state.