Electronic Spectroscopy of SmO in the 645 to 670 nm Range

The associative ionization reaction Sm + O → SmO⁺ + e^– is being investigated as an electron source that could transiently modify high-altitude electron densities via Sm vapor release. Electronic spectra have been obtained from tests where sounding rockets released Sm vapor, but the interpretation of these results has been hampered by the limited laboratory spectral data available for both SmO and SmO⁺. The present study extends the spectroscopic characterization of SmO in the 645–670 nm range, where the field data show the most prominent molecular emission features. Rotationally resolved excitation spectra, dispersed laser-induced fluorescence spectra, and fluorescence decay lifetimes are reported. The results are consistent with the assignment of a subset of the red-region bands to configurational transitions of the form Sm²⁺(4f⁵6s)O^2– ↔ Sm²⁺(4f⁵5d)O^2–. Analysis of the excited state hyperfine structure supports this configurational description.