Structure and internal rotation in the S(0) and S(1) states of o-toluidine studied by high resolution UV spectroscopy.

The rotationally resolved spectrum of the o-toluidine S(1)<-- S(0) origin was measured using laser induced fluorescence spectroscopy. From the resulting spectrum torsional barriers to internal rotation of the methyl group were derived, which resulted in S(0) state values of V(3) = 699 +/- 11 cm(-1) and V(6) = 64 +/- 11 cm(-1) with an effective rotational constant F of 5.38 +/- 0.04 cm(-1) while for the S(1) state the result was V(3) = 40.87 +/- 0.14 cm(-1) and V(6) = -16.8 +/- 0.8 cm(-1) with F = 5.086 +/- 0.001 cm(-1). The S(1) state structure was found to be severely distorted, with the methyl group making a 7.7 degrees degree angle with the benzene ring. Evidence of an excited state precessional motion of the methyl group was found.