VIBRATIONAL DYNAMICS OF LIQUIDS AND GLASSES PROBED WITH IR PHOTON-ECHOES

Vibrational photon echo experiments were performed on the asymmetric C O stretching mode of tungsten hexacarbonyl in the organic glasses di-b utylphthalate and 2-methylpentane as a function of temperature using i nfrared pulses from a free electron laser. The echo decays in DBP disp lay pronounced beats and are bi-exponential because the bandwidth of t he transform limited pulses exceeds the vibrational anharmonicity. Thi s leads to the excitation and dephasing of a multilevel coherence. Fro m the beat frequency, the anharmonicity is determined to be 14.7 cm(-1 ). From the bi-exponential decay components, the temperature-dependent vibrational dephasing, of both the v = 0 --> 1 and v = 1 --> 2 transi tions are determined. The temperature dependence of the homogeneous li newidth of the v = 0 --> 1 transition is measured for both liquids fro m 10 to 300 K. The homogeneous vibrational linewidth for W(CO)(6) in D BP and 2-MP both obey a power law temperature dependence below the gla ss transition temperature. In DBP, the vibrational linewidth is massiv ely inhomogeneously broadened even at room temperature; however, in 2- MP the line becomes homogeneously broadened at temperatures approachin g 300 K.