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

Absorption method has been applied to observe the collision-induced dipole transitions associated with the optically forbidden transitions 6_s ²¹S₀–6p²¹D₂, -6_s9d ¹D₂, -6_s10d ¹D₂, and -5d8p ¹D₂ of barium in argon, krypton or xenon atmosphere. The effective oscillator strength per unit rare-gas density is obtained to be, e.g., for 6s²–6s9d, 3.6×10⁻²⁴, 2.0×10⁻²³, and 5.8×10⁻²³cm³for 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.