Resonance Irradiation of Mercury Vapor in Nitrogen

A study has been made of phenomena related to the metastable $6{}_{}{}^3{}_{}{}^{}P_0^{}{}_{}{}^{}$ mercury atom appearing in a cell which contains nitrogen and saturated mercury vapor at 22°C and is irradiated with 2537 A ($6{}_{}{}^1{}_{}{}^{}S_0^{}{}_{}{}^{}-6\mathrm{}{}_{}{}^3{}_{}{}^{}P_1^{}{}_{}{}^{}$) resonance emission from a cool mercury arc. Various phenomena reported individually by many investigators are observed simultaneously and with improved techniques so that coherent correlations can be drawn and new conclusions developed. The relative $6{}_{}{}^3{}_{}{}^{}P_0^{}{}_{}{}^{}$ population produced from $6{}_{}{}^3{}_{}{}^{}P_1^{}{}_{}{}^{}$ atoms by inelastic collision is measured by self-absorption of 4047 A ($6{}_{}{}^3{}_{}{}^{}P_0^{}{}_{}{}^{}-7\mathrm{}{}_{}{}^3{}_{}{}^{}S_1^{}{}_{}{}^{}$); its dependence upon 2537 A intensity is linear and its dependence upon nitrogen pressure is given by theory. The $6{}_{}{}^3{}_{}{}^{}P_1^{}{}_{}{}^{}$ population is quenched by nitrogen. With conditions of high gas purity it is possible to produce large currents of heavy ions, the probable mechanism being a three-body collision between $6{}_{}{}^3{}_{}{}^{}P_0^{}{}_{}{}^{}$, $6{}_{}{}^3{}_{}{}^{}P_1^{}{}_{}{}^{}$, and ${\mathrm{N}}_2$ to form a highly excited molecule, which becomes ionized in a subsequent step. The ion formation is a volume process, varying with the second power of the 2537 A intensity. The continuum intensity near 4850 A is linear with 2537 A intensity and shows a pressure dependence consistent with molecular formation in a three-body collision between $6{}_{}{}^3{}_{}{}^{}P_0^{}{}_{}{}^{}$, $6{}_{}{}^1{}_{}{}^{}S_0^{}{}_{}{}^{}$, and ${\mathrm{N}}_2$. Mean lifetimes of metastable population, ion formation, and continuum intensity are measured as a function of pressure of nitrogen. They are found to differ distinctly, being generally larger in the order named. At high irradiation intensity an ion current of 405 μa was observed, leading to a prediction that several percent of the mercury atoms could be in the metastable state.