Electronic spectroscopy of organic acid dimers

The UV electronic spectroscopy of acetic, propionic, butyric, isobutyric acid, and their dimers is studied by measurements of the temperature and pressure dependence of their absorption spectra near 205 nm. The binding energy of each dimer is calculated using theoretical methods. The photo-absorption cross-sections for the monomer and dimer of each acid are calculated from 195–220 nm. The dimers are found to have a larger cross-section than the monomers and a peak absorbance that is shifted to higher energy. Theory and experiment are used to compare the strength of the hydrogen bonds in the ground and excited state of these dimers.