Infrared picosecond transient hole-burning studies of the effect of hydrogen bonds on the vibrational line shape

With infrared transient hole-burning spectroscopy we have investigated the influence of OD^.X hydrogen bonds on the vibrational line shape of O-D stretch vibrations in acid zeolites. The effect of hydrogen bonding on the line shape depends critically on the type of hydrogen bond. For hydrogen bonding in a rigid structure, the hydrogen bond determines the inhomogeneous linewidth, but the homogeneous linewidth is determined by coupling to a ^~200 cm^-l lattice mode as concluded from the temperature dependence of the dephasing rate. When the hydrogen bond is formed with an adsorbing molecule, the coupling between the high-frequency O-D stretch vibration and the low-frequency OD^.X hydrogen-bond stretching mode does determine the homogeneous linewidth. The difference between the two systems can be explained by the different hydrogen-bond potentials. Variation of the adsorbate provides a means of obtaining conclusive inforrnation on the coupling mechanism between the high-frequency O-D stretching mode and the low-frequency OD^.X hydrogen-bond stretching mode.