Bound-bound transitions in the emission spectra of Ba+-He excimer

We present an experimental and theoretical study of the emission and absorption spectra of the Ba⁺ ions and Ba^+*He excimer quasimolecules in the cryogenic Ba-He plasma. We observe several spectral features in the emission spectrum, which we assign to the electronic transitions between bound states of the excimer correlating to the 6 ²P_{3 /2} and 5 ²D_{3 /2 ,5 /2} states of Ba⁺. The resulting Ba⁺(5 ²D_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.