Multiphonon decay of stretch vibrations in zeolites

The vibrational dynamics of free and hydrogen bonded O-H and O-D groups in zeolites are investigated as a function of temperature with picosecond infrared saturation spectroscopy. From the temperature dependence of the population relaxation rare the order of the multiphonon relaxation process is obtained. It is noted that, in contrast with the conventional theory for vibrational relaxation of an oscillator in a dense medium, the absolute decay rate hardly scales with the number N of accepting modes. This leads us to conclude that, in addition to the order N of the relaxation process, the relaxation rate is also determined by the number of possible relaxation channels. From the temperature dependence of the decay rate of H-bonded oscillators we obtain insight in the role of H-bonding in vibrational relaxation in solids. It is found that the hydrogen bond efficiently accepts part of the oscillator energy in the relaxation process.