Knowledge Bank

The microwave spectrum of toluene $\bullet SO2$ has been observed using the FTMW technique. The spectrum displays a-, b- and c-type transitions. The transitions occur as doublets arising from the internal rotation of the methyl group. The transitions were fit using the Principal Axis Method (PAM) internal rotation Hamiltonian with a 3-fold symmetry potential barrier. The barrier height, $V3$, is 85 $cm-1$. The internal rotation spectra of toluene-$CD3\bullet SO2$ and toluene-$d8\bullet SO2$ were also assigned. For structural purposes the m = 0 transitions of toluene$\bullet S18O2$ and toluene$\bullet S16O18O$ were measured. Toluene$\bullet SO2$ has no plane plane of symmetry in its equilibrium geometry. The toluene and $SO2$ planes are approximately parallel; the distance, $Rcm$, joining their centers of mass is 3.37 {\AA}. The dipole moment of the complex is 1.87 D.