Knowledge Bank

The millimeter and submillimeter wave spectra of DSSD have been measured using a 6 ft free space cell. DSSD is a very slightly asymmetric top molecule ($K=-0.999992$) and its spectrum shows all the features of a $\perp$-type $transition.1$ The outstanding features of this type of rotational spectrum are the strong Q-branch absorption lines. From the assigned millimeter and submillimeter ground state Q-branch transitions of the $D32S32SD$ species, the band centers for the and branches are determined to be: All transitions originating from the $K\ne 0$ levels show the expected K-type splitting. Because of this and the fact that there is only a small difference between the rotational constants (C-B = -0.29 Mc/sec) the Q-branches have a rather complex structure. A simultaneous analysis of the Q-branch positions shows that the centrifugal distortion treatment with correction terms to $P6$ is not quite sufficient to account for the observed spectra. A similar result was obtained for $HSSH.2$ For the and branches the measurements were extended to the first excited states (torsional vibrational state $vt=1$ and the S-S bond stretching vibrational state $vo=1$). The internal rotational splitting of the ground state as well as the excited states is too small to be resolved, which is in agreement with our observations on HSSH.