Isotope effects in low-pressure Hg-rare-gas discharges.

Abstract

Measurements of the Hg (253.7 nm) output (${P}_{\mathrm{uv}}$) and output per arc watt (${P}_{\mathrm{uv}}$/${P}_{W}$) as a function of $^{196}\mathrm{Hg}$ concentration in a low-pressure Hg-Ar electrical discharge are reported. A peak increase of 7.9% and 6.8% for ${P}_{\mathrm{uv}}$ and ${P}_{\mathrm{u}\mathrm{v}/\mathrm{PW}}$, respectively, has been found at 2.6 wt. % $^{196}\mathrm{Hg}$. A modified Holstein-Biberman formalism that takes into account emission and absorption line shapes, energy transfer between Hg isotopes, rare-gas hyperfine mixing, and overlap between different isotopic components has been developed. Based on this formalism the calculated hyperfine structure (hfs) of the Hg(6 $^{3}P_{1}$\ensuremath{\rightarrow}6 $^{1}S_{0}$) transition is in very good agreement with our measured hfs. Furthermore our calculations predict a saturation in ${P}_{\mathrm{uv}}$ and ${P}_{\mathrm{uv}/{P}_{W}}$ for relatively low $^{196}\mathrm{Hg}$ concentrations. This formalism is applicable to various problems involving resonance radiation transfer in metal-vapor--rare-gas combinations containing more than one isotope.