Inelastic Collisions between Excited Alkali Atoms and Molecules. I. Sensitized Fluorescence and Quenching in Cs-N2and Cs-H2Systems

Excitation transfer between the $6 {}_{}{}^2{}_{}{}^{}P_{\frac{1}{2}}^{}{}_{}{}^{}$ and $6 {}_{}{}^2{}_{}{}^{}P_{\frac{3}{2}}^{}{}_{}{}^{}$ resonance states in cesium, induced by Cs-${\mathrm{N}}_2$ and Cs-${\mathrm{H}}_2$ collisions, was observed in the first experiment of its kind, in which techniques of sensitized fluorescence are used to investigate collisional mixing between resonance states of alkali atoms in mixtures with molecular gases. The cesium-vapor-gas system, in which the cesium vapor pressure was low enough to avoid radiation trapping, was irradiated with a single component of the resonance doublet. The fluorescent light, which contained both components of the doublet, was monitored at right angles to the direction of excitation. Measurements of relative intensities of the fluorescent components yielded the following cross sections for excitation transfer and for quenching of resonance radiation. For Cs-${\mathrm{N}}_2$ collisions: $Q_{12}({}_{}{}^2{}_{}{}^{}P_{\frac{1}{2}}^{}{}_{}{}^{}\to {}_{}{}^2{}_{}{}^{}P_{\frac{3}{2}}^{}{}_{}{}^{})=3.6\mathrm{}$ ${\mathrm{\AA }}^2$, $Q_{21}({}_{}{}^2{}_{}{}^{}P_{\frac{1}{2}}^{}{}_{}{}^{}\leftarrow {}_{}{}^2{}_{}{}^{}P_{\frac{3}{2}}^{}{}_{}{}^{})=16.2\mathrm{}$ ${\mathrm{\AA }}^2$, $Q_{10}({}_{}{}^2{}_{}{}^{}S_{\frac{1}{2}}^{}{}_{}{}^{}\leftarrow {}_{}{}^2{}_{}{}^{}P_{\frac{1}{2}}^{}{}_{}{}^{})=55.2\mathrm{}$ ${\mathrm{\AA }}^2$, $Q_{20}({}_{}{}^2{}_{}{}^{}S_{\frac{1}{2}}^{}{}_{}{}^{}\leftarrow {}_{}{}^2{}_{}{}^{}P_{\frac{3}{2}}^{}{}_{}{}^{})=63.5\mathrm{}$ ${\mathrm{\AA }}^2$. For Cs-${\mathrm{H}}_2$ collisions: