High-resolution cavity-enhanced absorption spectroscopy of SrO: Toward 90Sr detection

We report a high-resolution absorption spectroscopic study of SrO isotopologues aimed at enabling isotopic analysis of radioactive 90Sr. The A–X (1,0) band near 870 nm was investigated using cavity ring-down spectroscopy (CRDS), and the observed absorption lines, with sub-GHz full widths at half maximum (FWHM), allowed individual rovibrational transitions of the stable SrO isotopologues (88SrO, 87SrO, 86SrO, and 84SrO) to be resolved. From spectra covering approximately 350 GHz around the band head, molecular parameters necessary for predicting transition energies were estimated and subsequently used to predict the absorption spectrum of 90SrO. The peak amplitudes obtained by Gaussian fitting of the absorption lines showed excellent agreement with the natural abundance ratios, demonstrating the potential of CRDS for quantitative isotopic analysis of Sr. These results establish a methodology for applying high-sensitivity, high-resolution CRDS to molecules containing heavy metals, for which isotope shifts are intrinsically larger, allowing their absorption to be observed at longer wavelengths.