Tuning intramolecular anharmonic vibrational coupling in 4-nitroaniline by solvent-solute interaction.

Applying a combined experimental and theoretical approach we demonstrate that doublets of the nu(s)(NO(2)) band of 4-nitroaniline which have been observed in several environments originate from Fermi resonances. Changes of the line shapes typical for Fermi resonances are reported also for other isotopomers of 4-nitroaniline, however, for each of them in different solvents and solvent mixtures. Simulations of the infrared spectra based on the solvatochromic frequency shifts of the nu(s)(NO(2)) vibration determined experimentally together with calculated cubic couplings with overtones and combination bands account for the experimental findings.