We report the first spectroscopic detection of perdeuterated 1-oxadisulfane, DSOD, generated in a radio-frequency plasma of D 2 S and D 2 O. The chain molecule DSOD produces a perpendicular-type spectrum, with well-known spectral features encountered in previous studies of geometrically related molecules, such as compact Q-branches, which are clearly recognizable. The arrangement of the transitions shaping the Q-branches usually provides sufficient proof for a clear-cut detection of a chain molecule such as DSOD. Guided by quantum chemical calculations, we have located the band center of the r Q 2 -branch of DSOD in the frequency region near 466.5 GHz using the Cologne terahertz spectrometer. This r Q 2 -branch displays both b-and c-type spectra, quite analogous to the behavior of the corresponding r Q 2 -branch of HSOH. In addition, we have been able to detect an internal rotational splitting of $0.5 MHz for c-type transitions of the r Q 0 -branch, which lends independent support to our present assignment. From the measurements performed on Q-branches, we derive the following differences in rotational constants: A À ðB þ CÞ=2 ¼ 93331:001ð15Þ MHz, and ðB À CÞ=4 ¼ 172:95923ð29Þ MHz, in excellent agreement with theoretical predictions.