Laser spectroscopy of the A9-X8 transition of holmium monochloride

Using laser excitation spectroscopy, 18 red-degraded bands belonging to a single electronic transition of holmium monochloride have been observed in the 615-670 nm region. Thirteen of the bands, with vibrational levels 0?v^′?3 and 0?v″?4 have been obtained at high resolution and rotationally analyzed. Observation of the first lines in some of the bands has shown that Ω=8 in the ground state and Ω=9 in the upper state. By analogy with HoF, this transition has been labeled as A9-X8. The Ω=8 assignment for the X state establishes the ground state configuration of HoCl as Ho⁺(4f¹⁰6s²)Cl⁻, in accord with predictions of Ligand Field Theory. From the rotational analysis, the main equilibrium molecular constants of , for the upper state and , for the ground state have been obtained.