Knowledge Bank

The $0-0,1-0$, and 2-0 bands of the $\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}\Delta g-3\Sigma g$ electronic transition have been studied in liquid $O2$ and in liquid $O2-N2$ and $O2-A$ mixtures. Two cryostats were used; one enabled absorption to be observed for any path length up to 60 cm., the other for a fixed path length of 300 cm. In pure $O2$ the bands are broad with their intensities degraded towards higher frequencies. On dilution of the oxygen they become sharper and the $1-0$ and $2-0$ bands show two well defined components, the stronger of which is at the band origin, $\nu o$, as calculated from the constants for the free molecule. The frequency difference between the two components indicates that the weaker is due to simultaneous transitions in two oxygen molecules; one molecule makes the electronic transition together with the $0-0$ or $1-0$ vibrational transition and the other molecule makes only the 1-0 vibrational transition of the ground electronic state. The integrated absorption coefficient of the bands varies in a complex way with increasing dilution. The behaviour of the bands in the gas phase at high pressures will also be discussed.