Spectroscopic study of jet-cooled heterodimers of salicylic acid with acetic and trifluoroacetic acids

The photophysical properties of the intermolecular hydrogen-bonded complexes of salicylic acid with acetic acid and trifluoroacetic acid have been investigated in a supersonic expansion. The fluorescence excitation spectra are characterized by a long harmonic progression upon a low frequency mode and their origin is blue-shifted with respect to that of pure salicylic acid. The emission spectra exhibit a single broad band peaking at 360 and 390 nm respectively for the complex with trifluoroacetic and acetic acids and are not dependent on the excitation wavelength. The results have been rationalized in terms of a single minimum energy curve in both the ground and excited states.