Collisional broadening of alkali doublets by helium perturbers

Abstract

We report results for the Lorentzian profiles of the Li I, Na I and K I doublets and the Na I subordinate doublet broadened by helium perturbers for temperatures up to 3000 K. They have been obtained from a fully quantum-mechanical close-coupling description of the colliding atoms, the Baranger theory of line shapes and new ab initio potentials for the alkali–helium interaction. For all lines except the 769.9 nm K I line, the temperature dependence of the widths over the range 70 ≤ T ≤ 3000 K is accurately represented by the power law form w = aTbb with 0.38 < b < 0.43. The 769.9 nm K I line has this form for 500 ≤ T ≤ 3000 K with b having the higher value of 0.49. Although the shifts have a more complex temperature dependence, they all have the general feature of increasing with temperature above T ~ 500 K apart from the 769.9 K I line whose shift decreases with temperature.