Spectroscopic characterization of ytterbium monohalide emission in a high pressure electrodeless microwave arc discharge

Molecular emission has been observed in high-pressure electrodeless microwave arc discharges from the monochloride, monobromide, and monoiodide of ytterbium. The vibrational analyses of the electronic transitions in YbBr and YbI represent the first spectroscopic data for these molecules. Emission from the A (2Σ1/2) →X (2Π+) and A (2Π+) and R (2Π3/2) →X (2Σ+) transitions in YbCl have been observed. By analogy with YbF and YbCl, the blue degraded emission in YbBr and YbI has been assigned to the A (2Π1/2) →X (2Σ+) and A (2Π3/2) →X (2Σ+) transitions. The term values for YbBr and YbI are shifted to the red with respect to YbCl by <100 cm−1 and <300 cm−1, respectively, for both transitions. The spin–orbit coupling constants of the A (2Π) state in YbBr and TbI have been determined from the difference in the band origins of the two A→X transitions. The effect of the lanthanide contraction in the ytterbium monohalides has been examined by comparing the ground state vibrational frequencies of the ytterbium monohalides and the Group IIa monohalides. Finally, the spectra of YbCl observed under high-pressure arc conditions have been compared to the YbCl emission previously observed in a low-pressure chemiluminescent beam experiment.