Abstract

Since hydrogen bonds play a key role in chemistry and biology there is a great interest in hydrogen-bonded molecules. Simple examples for such systems are fatty acid dimers. Their binding enthalpies are on the order of 60 kJ/mole, which means that both monomers and dimers are present at room temperature and normal conditions. Fatty acid molecules are thus well suited to study chemical equilibrium reactions. Numerous investigations, including spectroscopic studies, for the determination of the dimerization enthalpy AH have been reported. However, previous measurements were all performed on stationary gas mixtures with the disadvantage of possible adsorption effects that would distort the equilibrium between monomers and dimers if the partial pressure changes during a typical measurement time of one or two hours. Here we present the first spectroscopic measurements on flowing gas mixtures that avoid the problems associated with wall adsorption. Furthermore, integrated line intensities of most fatty acid molecules, particularly of dimers, are not known. Our studies permit the direct determination of line intensities that are of great interest for comparison with NMR data and thus, e.g., for the investigation of the vibration-supported tunneling of protons in dimers.¹

© 1994 IEEE