THE ROTATIONAL SPECTRUM OF SH AND SD

With the Cologne terahertz spectrometer, the lower J rotational spectr um of the SD radical has been detected for the first time in the labor atory, in analogy with our previous recent detection of the SH radical . The radicals were produced by discharging H2S (D2S) buffered with He and H-2 (D-2). The spectra were analyzed employing Hund's case (a) co upling scheme. The SH radical has an inverted (2) Pi state, as does OH , so that the (2) Pi(3/2) state is the energetically lower one. For bo th SH and SD, the rotational and centrifugal distortion constants, the spin orbit, the spin rotation, the R-doublet, and the hyperfine inter action constants were determined by combining the newly acquired exper imental data with those available in the literature. The rotational co nstant B-0 for SD is 146885.297 (26) MHz, while our latest value for S H is 283587.62 (12) MHz (the values in parentheses denote the calculat ed uncertainty obtained by a least-squares fit). The SH radical and it s deuterated isotopomer may be detectable in interstellar space becaus e of the high cosmic abundance of elemental sulfur and the high abunda nce of H2S. Since the (2) Pi(1/2) electronic state lies nearly 400 cm( -1) above the (2) Pi(3/2) state, the rotational transitions in the (2) Pi(1/2) state should only be detectable in hot interstellar sources, and they are potentially good indicators of star formation.