Enhancement of the vibrational relaxation rate of surface hydroxyls through hydrogen bonds with adsorbates

With time-resolved (picosecond) infrared saturation spectroscopy new information is obtained about the interaction of zeolite surface hydroxyls with small adsorbed molecules. It is found that the presence of the adsorbate, which is weakly hydrogen bonded to the zeolite hydroxyl, causes the vibrational lifetime of the zeolite hydroxyl to decrease. Remarkably, this enhancement of the de-excitation is neither due to energy transfer to internal degrees of freedom of the adsorbed species nor into a one-photon desorption process. Rather, it is due to an increased coupling of the hydroxyl stretching mode to its accepting modes.