ROTATIONAL SPECTRUM, STRUCTURE, AND INTERNAL DYNAMICS OF THE $C_{6}H_{6}-H_{2}S$ DIMER

Author Institution: Noyes Chemical Laboratory, University of Illinois; Department of Chemistry, Indian Institute of TechnologyTwo symmetric top progressions $(K^{2})$ were observed for isotopomers of the $C_{6}H_{6}-H_{2}S$ dimer with axial symmetry, using the Illinois pulsed nozzle, Balle/Flygare FTMW spectrometer as modified. The rotational constants B, $D_{j}$ and $D_{jk}$ 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 $D_{j}$ is numerically larger and negative, $-13.80$ kHz. Also $D_{jk}$ is much larger, 75.7 kHz. aid higher order (H) terms were required to fit the data. In addition rotational spectra were obtained for $C_{6}H_{6}-H_{2}^{34}S, C_{6}H_{6}-HDS C_{6}H_{6}-HDS, C_{6}H_{6}-D_{2}S$, and $^{13}CC_{5}H_{6}-H_{2}S$. Some observations were made on $C_{6}H_{6}-H_{2}{^{33}}S$, giving J and K dependent values for $\chi_{aa}(^{33}S)$ in the lower and upper slates of about 18 and 10 MHz (signs undetermined). A weak third progression was observed for $C_{6}H_{6}-H_{2}S$ with upto (2K + 1) irregular components at each J and with B-1181 MHz. Analysis of the data indicates that the $H_{2}S$ is located on the $C^{6}$ axis of the benzene with a c.m. $(C_{6}H_{6})$ 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 $0_{00}$ and $1_{01}$ ``free” rotor states of the $H_{2}S$. The third progression is presumably a third rotor state of the $H_{2}S$. The results are compared with earlier work on $C_{6}H_{6}-H_{2}O$. We thank C. E. Dykstra and G. T. Fracer for helpful discussions and suggestions