We present an experimental and theoretical study of the emission and absorption spectra of the Ba$^{ +}$ ions and Ba$^{ +\ast}$He excimer quasimolecules in the cryogenic Ba--He plasma. We observe several new spectral features in the emission spectrum which we assign to the electronic transitions between bound states of the excimer correlating to the 6$^{ 2}P_{ 3/2}$ and 5$^{ 2}D_{ 3/2,5/2}$ states of Ba$^{ +}$. The resulting Ba$^{ +}$(5$^{ 2}D_{ J}$)He is a metastable electronically excited complex with orbital angular momentum $L$=2, thus expanding the family of known metal--helium quasimolecules. It might be suitable for high-resolution spectroscopic studies and for the search for new polyatomic exciplex structures.
Categories: physics.atom-ph