Spectroscopy of barium ions in He II

Abstract The excitation and emission spectra of Ba + immersed in superfluid helium have been measured. The two absorption bands - several nm wide — are slightly blue shifted with respect to the D 1 and D 2 lines of the free ion. Three emission bands at λ 1 = 491 nm, λ 2 = 523 nm and λ 3 = 648 nm have been observed.