Observation of collision-induced-dipole absorption bands in strontium-rare-gas mixtures. I. The 5s-4d bands

Reduced absorption coefficients have been measured for the collision-induced-dipole (CID) absorption bands associated with the 5s-4d transition of atomic strontium perturbed by He, Ne, Ar, Kr, Xe, and Sr. The main CID absorption band, assigned to 5sΣ-4dΣ, extends from the position of the atomic 5s-4d transition towards the shorter-wavelength side for every perturber. For Xe and Kr, an additional small absorption band is seen at the foot of the atomic 5s-4d transition. The former 5sΣ-4dΣ band is interpreted to result from collisional mixing of the 5p state of atomic Sr into the molecular 4dΣ state for small internuclear separations, while the latter band is interpreted to result from the collisional quadrupole (strontium)-dipole (Xe or Kr) interaction.