Rotationally resolved fluorescence excitation spectra of several torsionally active bands in the S-1-S-0 electronic transitions of toluene and toluene-d(3) have been recorded in the collision-free environment of a molecular beam. Analyses of these data provide accurate values of the internal rotor constants F; the barrier heights V-6; the frame rotational constants A(F); the overall rotational constants B and C; and the torsion-rotation coupling constants A(F)'; in the m = 0 and m = +/- 1 levels of the S-0 state and the m = 0, +/- 1, and 3+ levels of the S-1 state. Comparison of the A(F), B, and C values in the m = 0 levels of the two states shows that S-1 toluene is quinoidal in form, with shorter ring "parallel" C-C bonds than "perpendicular" ones, unlike the S-0 state. The preferred conformation of the methyl group is staggered in both states, but the V-6 values are significantly different; V-6(S-0) = -4.874 and V-6(S-1) = -26.376 cm(-1). Comparison of the F, A(F), and A(F)' values in the different torsional levels of the S-1 state shows that, below the barrier, the methyl group tilts and the ring bond lengths change with increasing displacements along the torsional coordinate. Above the barrier, the precessional motion of the CH3 is quenched but larger ring distortions are observed. Thus, the data are consistent with an enhanced hyperconjugative interaction between the benzene ring and the methyl group in the S-1 state. This interaction is substantially modulated by the relative motion of the two attached groups, providing a facile route to IVR.