S ₁ –S ₀ Electronic spectrum of jet-cooled m-aminophenol

The S1 and S0 states of m-aminophenol have been investigated using laser induced fluorescence and dispersed fluorescence spectroscopy in a supersonic jet. The dispersed fluorescence spectra, obtained by exciting the bands at 34 109 and 34 469 cm−1, show the same vibronic structure, which suggests the coexistence of rotational isomers in m-aminophenol. A quantum chemical calculation also supports the coexistence of rotational isomers. From the relative intensities in the spectrum and the calculated stabilization energies of isomers, the bands are assigned to the origin of the cis- and trans-isomers, respectively. The dispersed fluorescence spectra obtained by exciting the S1 vibronic bands were analyzed by comparing with the calculated vibrational frequencies and IR and Raman spectra. From the analysis, the S1 vibronic bands have been assigned. It was found that a one-to-one correspondence between the S1 and S0 vibrations is broken, and vibrational mixing due to Fermi resonance or the Duschinsky effect is suggested.