Millimeter Wave Rotational Spectrum of HSSH and DSSD. III. Q Branches of DSSD

The Q branches of the $\text{K=2← 1}$ and $\text{K=3← 2}$ rotational subbands of the ground state of D³²S³²SD have been measured in the frequency range 200–350 GHz. The locations of the subband centers have been determined to be at ${\nu }_0^{\text{(1)}}\text{=209\hspace{0.17em}741.9± 0.1}$ MHz and ${\nu }_0^{\text{(2)}}\text{=349\hspace{0.17em}544.5± 0.1}$ MHz for the $\text{K=2← 1}$ and $\text{K=3← 2}$ rotational subbands, respectively. The most prominent and unusual feature encountered in the spectra of the ^rQ₁ and ^rQ₂ branches is that the observed K doubling of the $\text{K=3← 2}$ rotational lines is larger than the K doubling of the $\text{K=2← 1}$ Q‐branch transitions of the same J value. This anomalous K doubling of the Q branches is shown to be caused by the superposition of two contributing effects, the asymmetry splitting and centrifugal‐distortion splitting. This concept has been established in the preceding paper. For the K=1 levels both contributions to the K doubling are equally important, while for the K=2 levels the K doubling is entirely due to the centrifugal‐distortion splitting. The analysis of a total of some 350 measured and assigned absorption lines indicates clearly that together with the three rotational constants, six quartic distortion constants are sufficient to explain the spectrum. A discussion of the spectra of ^rQ_Ka branches for $K_a\text{≥ 3}$ is given, although these transitions have not been observed.