Mean Lives of Lines of Mercury Triplet2P0123−2S13

Abstract

The mean life of each of three lines coming from the same upper level in the mercury atom has been measured. The triplet $2{}_{}{}^3{}_{}{}^{}P_{012}^{}{}_{}{}^{}-2{}_{}{}^3{}_{}{}^{}S_1^{}{}_{}{}^{}$ was excited by electron impact under conditions involving negligible ionization and concentration of excited atoms. The method was that previously described by Webb, in which high frequency voltages are applied in phase to the excitation and detecting systems. The lines were excited in a sealed-off tube with mercury pressures between 0.004 and 0.03 mm. The exciting voltage was less than ten volts. The excitation was such that there was no appreciable concentration in the $2P$ states. A specially designed potassium-hydride photoelectric cell was used as the detecting system. Optical filters were used to isolate the line measured. The results agree with the assumption that the radiation decays exponentially after impact. For the lines $\lambda 4047$ and $\lambda 4358$ the lives were found to be the same within the experimental error (0.75 percent) viz. $\tau =5.75\mathrm{}\times {10}^{-8\mathrm{}}$ secs. The value for $\lambda 5461$ was four times greater, $\tau =2.37\mathrm{}\times {10}^{-7\mathrm{}}$ secs. The agreement between the lives of $\lambda 4047$ and $\lambda 4358$ supports the quantum assumption that lines coming from the same level in the atom have the same life. Collins has found that under certain exciting conditions the fine-structure of $\lambda 5461$ is anomalous as compared to $\lambda \lambda 4047$ and 4358. It is suggested that the longer life found for $\lambda 5461$ may be explained by considering the fine structure of the $2{}_{}{}^3{}_{}{}^{}S_1^{}{}_{}{}^{}$ level. The results are then consistent with the above assumption.