VIBRATIONAL ANHARMONICITY AND MULTILEVEL VIBRATIONAL DEPHASING FROM VIBRATIONAL ECHO BEATS

Vibrational echo experiments were performed on the IR active CO stretc hing modes (similar to 2000 cm(-1)) of rhodium dicarbonylacetylacetona te [Rh(CO)(2)acac] and tungsten hexacarbonyl [W(CO)(6)] in dibutylphth alate and a mutant of myoglobin-CO (H64V-CO) in glycerol-water using p s IR pulses from a free electron laser. The echo decays display pronou nced beats and are nonexponential. The beats and nonexponential decays arise because the bandwidths of the laser pulses exceed the vibration al anharmonicities, leading to the excitation and dephasing of a multi level coherence. From the beat frequencies, the anharmonicities are de termined to be 14.7, 13.5, and 25.4 cm(-1), for W(CO)(6), Rh(CO)(2)aca c, and H64V-CO, respectively. From the components of the nonexponentia l decays, the vibrational dephasing at very low temperature of both th e upsilon = 0-1 and upsilon = 1-2 transitions are determined. At the l owest temperatures, T-2 approximate to 2T(1), so the upsilon = 2 lifet imes are obtained for the three molecules. These are found to be signi ficantly shorter than the upsilon = 1 lifetimes. Although the upsilon = 1 lifetimes are similar for the three molecules, there is a wide var iation in the upsilon = 2 lifetimes. (C) 1997 American Institute of Ph ysics.