2024ApJ...965...46A

Seven rotational and fine-structure transitions of the deuterated molecular ion SD⁺ in the X³Σ^– ground electronic state have been measured in the 271-863 GHz region in the laboratory. This ion has been produced by direct-current glow discharge using a mixture of D₂S and argon in a free space cell in a temperature range of -140°C to -160°C. The rotational, centrifugal distortion, spin-spin interaction, and hyperfine constants have been determined; the standard deviation of the residuals in the fitting is 109 kHz. The set of obtained spectroscopic parameters provides a list of accurate submillimeter rest frequencies of SD⁺ for astronomical detection. We have investigated lines of SD⁺ toward the quasar PKS 1830-211 using the Atacama Large Millimeter/submillimeter Array archive, as the z = 0.89 molecular absorber exists in front of this quasar. A data set covering the 297 GHz region includes the N_J = 2₃-1₂ transition at 561 GHz due to redshift, providing an upper limit of the column density N_tot = 3 × 10¹² cm^–2 for SD⁺.