Mid-infrared absorption spectrum of 5,6-dihydroxyindole-2-carboxylic acid

Combining mid-infrared spectroscopy and ab initio density-functional calculation, this letter clarifies vibrational modes corresponding to dominant infrared active absorption bands of 5,6-dihydroxyindole-2-carboxylic acid. The impact of intra- and/or intermolecular hydrogen bonds on vibrational frequencies is also discussed.