Foreign gas broadening and shift of the strongly “forbidden” lead line at 1278.9Â nm

The collisional broadening and shift rate coefficients of the “forbidden“ 6p2 3P0 → 6p2 3P1 transition in lead were determined by diode laser absorption measurements performed simultaneously in two resistively heated hot-pipes. One hot-pipe contained Pb vapor and noble gas (Ar or He) at low pressure, while the other was filled with Pb and noble gas at variable pressure. The measurements were performed at temperatures of 1220 K and 1290 K, i.e., lead number densities of 4.8 × 1015 cm− 3 and 1.2 × 1016 cm− 3. The broadening rates were obtained by fitting the experimental collisionally broadened absorption line shapes to theoretical Voigt profiles. The shift rates were determined by measuring the difference between the peak absorption positions in the spectra measured simultaneously in the heat pipe filled with noble gas at reference pressure and the one with noble gas at variable pressure. The following data for the broadening and shift rate coefficients due to collisions with Ar and He were obtained: γBAr = (3.4 ± 0.1) × 10− 10 cm3 s− 1, γBHe = (3.8 ± 0.1) × 10− 10 cm3 s− 1, γSAr = (− 7.3 ± 0.8) × 10− 11 cm3 s− 1, γSHe = (− 6.5 ± 0.7) × 10− 11 cm3 s− 1.