The effect of rare-gas collisions on the wings of the potassium 4p2P3/2-7s2S1/2(5802 Å) transition

The potassium 4p 2 P 3/2 -7s 2 S 1/2 (5802 Å) transition when broadened by the noble gases exhibits satellites and line asymmetries which are clearly of a collisional origin. Measurements of complete line profiles are given for broadening by He, Ne, Ar, Kr and Xe within 16 cm -1 of the line centre at densities up to 10 19 atoms cm -3 as observed for a microwave-excited electrodeless discharge. These are compared to computed unified theory line shapes and are found to agree when appropriate parameterised potentials are chosen for the potassium-noble-gas interactions. Such analyses yield experimental potentials for the 7s state that show extrema at interatomic separations from 14 to 18 Å that are slightly repulsive for He and Ne, and attractive for Ar, Kr, and Xe. These features are not correctly predicted by the pseudopotential calculations of Pascale and Vandeplanque (1974) and are only qualitatively accounted for with potentials of the Fermi type.