Fano coupling in perturbed solid acid hydroxyls

A simple analytical expression for the Evans window in the infrared absorption spectrum of hydrogen‐bonded basic molecules in protonic zeolites is presented. The expression shows that the essential parameters are the position of the shifted “uncoupled” OH stretching frequency, its width, the position of the in‐plane bending overtone and the coupling of this mode with the OH stretching mode. Analysis of the Fermi resonances in the OH stretching band profile provides a method to determine whether adsorbed molecules are hydrogen bonded or protonated.