Knowledge Bank

Two symmetric top progressions $(K2)$ were observed for isotopomers of the $C6H6-H2S$ dimer with axial symmetry, using the Illinois pulsed nozzle, Balle/Flygare FTMW spectrometer as modified. The rotational constants B, $Dj$ and $Djk$ found upper state of the parent special are 1368.538 MHz, and 1.44 and 13.63 kHz. B for the lower state is 1140.580 MHz, not much smaller, but $Dj$ is numerically larger and negative, $-13.80$ kHz. Also $Djk$ is much larger, 75.7 kHz. aid higher order (H) terms were required to fit the data. In addition rotational spectra were obtained for $C6H6-H234S,C6H6-HDSC6H6-HDS,C6H6-D2S$, and $\mathrm{<mrow\; data-mjx-texclass="ORD">13</mrow>}CC5H6-H2S$. Some observations were made on $C6H6-H2\mathrm{<mrow\; data-mjx-texclass="ORD">33</mrow>}S$, giving J and K dependent values for $\chi aa(33S)$ in the lower and upper slates of about 18 and 10 MHz (signs undetermined). A weak third progression was observed for $C6H6-H2S$ with upto (2K + 1) irregular components at each J and with B-1181 MHz. Analysis of the data indicates that the $H2S$ is located on the $C6$ axis of the benzene with a c.m. $(C6H6)$ to S distance of 3.82 {\AA} and both protons closer to die ring than S. The upper and lower progressions are attributed respectively to $000$ and $101$ ``free” rotor states of the $H2S$. The third progression is presumably a third rotor state of the $H2S$. The results are compared with earlier work on $C6H6-H2O$. We thank C. E. Dykstra and G. T. Fracer for helpful discussions and suggestions.