Knowledge Bank

$Ar+$ - laser excitation has been used to pump several vibrational bands in the $\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}Au\leftarrow 1Ag$ electronic transition of glyoxal. The laser band-width restricts each excitation to $\approx 10-15$ rotational levels of the $\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}Au$ state. Fluorescence after excitation to the level $v\prime 7=1$ shows features due to yibrational relaxation to the $0\circ$ state at pressures as low as $5\times 10-4$ Torr. At this pressure no appreciable rotational relaxation can be observed within the $71$ state but the rotational structure of the $0\circ$ O emission band indicates that rotational quantum number changes have accompanied vibrational relaxation. Strong propensity rules for $\Delta K$ are observed. Fluorescence after pumping the aero point level directly shows little evidence of rotational equilibration even at pressures up to $10-2$ Torr. The course of rotational energy transfer has been followed as a function of pressure. Collision-induced intersystem crossing is found to compete effectively with rotational and vibrational relaxation.