Kd. Rector et al., VIBRATIONAL ANHARMONICITY AND MULTILEVEL VIBRATIONAL DEPHASING FROM VIBRATIONAL ECHO BEATS, The Journal of chemical physics, 106(24), 1997, pp. 10027-10036
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.