Knowledge Bank

A Nitrogen-laser-pumped tunable liquid dye laser has been used to populate the first excited singlet state ($\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}Au$) of glyoxal. The collision-free lifetime of the $\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}Au$ state has been measured to be 2.24 $\mu$sec. The collisional efficiencies which have been measured for deactivation of the $\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}Au$ state appear to be relatively insensitive to the nature of the collision partner (He, Ar, Xe, $Dz$, $Oz$) suggesting little, if any, “heavy atom” effect. The collisional deactivation of the $\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}Au$ is accompanied by activation of the $\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}Au$ state, indicating considerable intersystem crossing. The lifetime of the $\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}Au$ state, 1.78 msec, is independent of rare gas pressure over the pressure range 0-70 Torr. However this triplet state is found to be effectively quenched by oxygen with a collisional rate of 3.15 $msec-1$ $torr1$. These preliminary experiments demonstrate the powerful potential of laser excitation as a tool for the study of excited-state dynamics.