Structure and internal rotation in the S0 and S1 states of o-toluidine studied by high resolution UV spectroscopy

Abstract

The rotationally resolved spectrum of the o-toluidine S₁← S₀ 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 S₀ state values of V₃ = 699 ± 11 cm⁻¹ and V₆ = 64 ± 11 cm⁻¹ with an effective rotational constant F of 5.38 ± 0.04 cm⁻¹ while for the S₁ state the result was V₃ = 40.87 ± 0.14 cm⁻¹ and V₆ = −16.8 ± 0.8 cm⁻¹ with F = 5.086 ± 0.001 cm⁻¹. The S₁ state structure was found to be severely distorted, with the methyl group making a 7.7° degree angle with the benzene ring. Evidence of an excited state precessional motion of the methyl group was found.