High-resolution laser excitation spectroscopy of the B̃²Σ⁺-X̃²Σ⁺ system of jet-cooled SrOD

The high-resolution laser excitation spectrum of the 001-000 and 000-000 bands of the B̃²Σ⁺-X̃²Σ⁺ transition of SrOD was recorded. The SrOD molecules were made by pulsed laser ablation of Sr metal followed by reaction with D₂O. Sub-Doppler resolution and rotational cooling were achieved by expansion into vacuum and excitation with a cw dye laser perpendicular to the molecular beam. A molecular linewidth of 200 MHz and the lack of spectral congestion allowed a Q branch to be detected. Spin-orbit mixing between the Ã²Π and B̃²Σ⁺ states caused the unusual appearance of a moderate intensity Q branch in a nominally parallel ²Σ⁺-²⁺ transition. From the relative intensities of the rotational lines, the ratio of the perpendicular to the parallel transition dipole moment was found to be 0.2 to 0.3.