Experimental Determination of the De-excitation Cross Section for the6P13State of Mercury by Thallium

The de-excitation or quenching cross section of thallium for the $6{}_{}{}^3{}_{}{}^{}P_1^{}{}_{}{}^{}$ state of mercury has been obtained over a range of temperatures of 800 to 900°C. Comparison of the resonance fluorescence from a mercury-thallium vapor mixture with the resonance fluorescence from a pure mercury vapor at the same number density, as determined by line absorption, allows the calculation of the de-excitation cross section. The present data together with Garrett's value of the lifetime of the $6{}_{}{}^3{}_{}{}^{}P_1^{}{}_{}{}^{}$ state of mercury and existing data on the vapor pressures of mercury and thallium were used to obtain values of the de-excitation cross section. Values of the cross section range from 108±41 ${\mathrm{\AA }}^2$ at 800°C to 80±19 ${\mathrm{\AA }}^2$ at 900°C. The corresponding quenching-rate coefficients varied from (5.1±1.9)×${10}^{-7\mathrm{}}$ ${\mathrm{cm}}^3$/sec at 800°C to (4.0±0.9)×${10}^{-7\mathrm{}}$ ${\mathrm{cm}}^3$/sec at 900°C.