THE TRIPLET STATES OF BIACETYL AND ENERGY TRANSFER AS REVEALED BY OPTO-ACOUSTIC SPECTROSCOPY

Author Institution: Bell LaboratoriesUsing the technique of opto-acoustic spectroscopy, it is first demonstrated that radiationless decay from $S_{1}$ of biacetyl, when excited at wavelengths longer than 4430 {\AA}, involves a very slow $(k_{nr} \sim 10^{3}sec^{-1})$ $T_{1}\rightarrow $sO step, whereas beyond this wavelength a second fast channel opens: $T_{2}\rightarrow $SO. Addition of oxygen makes the apparent $T_{1}\rightarrow $So relaxation very fast. In mixtures of biacetyl and benzene, monitoring the slow component of the heat released from the biacetyl $T_{1}$ state while irradiating at wavelengths absorbed by benzene shows that energy transfer from benzene directly to the $T_{n}$ manifold of biacetyl occurs from the onset of $^{1}B_{2u}$ absorption to 2440 {\AA}, rather than throughout the band. In pyridine-biacetyl mixtures, the lowest $n \rightarrow\Pi^{*}$ state of pyridine transfers to the triplet manifold of biacetyl, but the lowest $\Pi \rightarrow \Pi^{*}$ state does not