Knowledge Bank

Using the technique of opto-acoustic spectroscopy, it is first demonstrated that radiationless decay from $S1$ of biacetyl, when excited at wavelengths longer than 4430 {\AA}, involves a very slow $(knr\sim 103sec-1)$ $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 $T1$ state while irradiating at wavelengths absorbed by benzene shows that energy transfer from benzene directly to the $Tn$ manifold of biacetyl occurs from the onset of $\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}B2u$ absorption to 2440 {\AA}, rather than throughout the band. In pyridine-biacetyl mixtures, the lowest $n\to \Pi \ast$ state of pyridine transfers to the triplet manifold of biacetyl, but the lowest $\Pi \to \Pi \ast$ state does not.