Collision-Induced Dipole Transitions Associated with High-Lying States. I. Absorption Studies of Barium in Rare Gases

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Abstract
Absorption method has been applied to observe the collision-induced dipole transitions associated with the optically forbidden transitions 6 s 2 1 S 0 -6 p 2 1 D 2 , -6 s 9 d 1 D 2 , -6 s 10 d 1 D 2 , and -5 d 8 p 1 D 2 of barium in argon, krypton or xenon atmosphere. The effective oscillator strength per unit rare-gas density is obtained to be, e.g. , for 6 s 2 -6 s 9 d , 3.6×10 -24 , 2.0×10 -23 , and 5.8×10 -23 cm 3 for argon, krypton, and xenon, respectively. A correlation is found between the effective oscillator strength and the scattering length of the rare-gas atoms for electrons. This is explained from a model in which an adjacent P state mixes into the D state due to the interaction potential between the loosely-bound valence electron and the rare-gas atom.