The Quenching of Mercury Resonance Radiation by Foreign Gases

Abstract

The intensity of emitted resonance radiation from Hg vapor is decreased as the pressure of an admixed gas increases. The following cycle of transitions occurs for the rare gases or nitrogen. Absorption of $\lambda 2537$ produces ${}_{}{}^3{}_{}{}^{}P_1^{}{}_{}{}^{}$ Hg' atoms. Some of these return to the $1S_0$ state by radiating and a portion of this radiation escapes to be observed as resonance. The rest is reabsorbed in the vapor producing more ${}_{}{}^3{}_{}{}^{}P_1^{}{}_{}{}^{}$ atoms. Some of the ${}_{}{}^3{}_{}{}^{}P_1^{}{}_{}{}^{}$ atoms undergo collision of the second type with foreign gas molecules resulting in ${}_{}{}^3{}_{}{}^{}P_0^{}{}_{}{}^{}$ atoms. A large fraction of these atoms return to the ${}_{}{}^3{}_{}{}^{}P_1^{}{}_{}{}^{}$ state by collision of the first type with high speed gas molecules. At 18°C one collision in 6000 satisfies the condition of conservation of energy and momentum requisite to such an energy transfer. Other ${}_{}{}^3{}_{}{}^{}P_0^{}{}_{}{}^{}$ atoms return to the normal state through collision with traces of hydrogen impurities in which the energy of the mercury atom is utilized in the dissociation of ${\mathrm{H}}_2$. Still other ${}_{}{}^3{}_{}{}^{}P_0^{}{}_{}{}^{}$ atoms collide with normal Hg atoms producing ${\mathrm{Hg}}_2$' excited molecules. This cycle of transitions is completely developed from kinetic theory considerations in which every collision, except in the molecular formation, is considered as effective. All the constants may be computed directly. Concentrations of the ${}_{}{}^3{}_{}{}^{}P_0^{}{}_{}{}^{}$ state as high as one part in a few hundred may be readily obtained under moderately intense illumination.