TOLUENE INTERNAL ROTATION: REFINED BARRIER HEIGHT IN $S_{1}$. SIGN OF $V_{6}$, AND MOTION ALONG THE TORSIONAL $COORDINATE.^{a}$

$^{a}$ Work supported by NSFAuthor Institution: Department of Chemistry, University of PittsburghHigh resolution electronic spectra of three torsional bands in the $S_{1}\leftarrow S_{0}$ electronic transition of toluene have been recorded in a molecular beam. The analyses of these spectra provide a unique and unambigious determination of the sign of the $V_{6}$ hindering potential in both electronic states; $V_{6}(S_{0}) = -4.874 cm^{-1}$ and $V_{6}(S_{1})= -26.375 cm^{-1}$. Furthermore, the data show that both F and the frame rotational constant $A_{F}$ vary between torsional levels within the $S_{1}$ manifold. Information about geometric changes responsible for these differences will be discussed, along with the validity of the one-dimensional, rigid frame-rigid top model