Measurement of the Life of the Metastable Mercury Atom

Abstract

Half value time for the $2^3$ ${\mathrm{P}}_0$ state of Hg for various pressures of admixed ${\mathrm{N}}_2$— A high speed rotating disk has been used to interrupt the total radiation from a water-cooled and magnetically controlled quartz mercury arc before optically exciting mercury vapor in a quartz resonance tube at room temperature. In the neighborhood of ${10}^{-4\mathrm{}}$ sec. after the optical excitation a flash of visible radiation from another water-cooled and magnetically controlled mercury arc was passed through the resonance tube and the absorption spectrum photographed. The line 4047 ($2{}_{}{}^3{}_{}{}^{}P_0^{}{}_{}{}^{}-2\mathrm{}{}_{}{}^3{}_{}{}^{}S_1^{}{}_{}{}^{}$) showed strong absorption when a few millimeters of nitrogen were introduced into the resonance tube. The lines 4077, 4358, 5461, 5770 and 5790 showed no measurable absorption under similar conditions. The rate of decay of the amount of 4047 absorbed with respect to the time-wait after excitation of the mercury vapor was taken as the rate of decay of the metastable $2{}_{}{}^3{}_{}{}^{}P_0^{}{}_{}{}^{}$ state. The life or half-value time of the state was found to vary markedly with the pressure of admixed nitrogen. The maximum life 4.2×${10}^{-4\mathrm{}}$ sec. occurred for 6.8 mm of nitrogen. No absorption of 4047 was observed upon the introduction of hydrogen, argon, neon, or helium into the resonance tube.