Investigating pure vibrational dephasing of I3- in solution:: Temperature dependence of T2* for the fundamental and first harmonic of ν1

Pure nu(1) vibrational dephasing of triiodide is recorded in ethanol and methyl-tetrahydrofurane solutions from 300 to 100 K, for the vibrational fundamental and its first overtone. Using impulsive Raman spectroscopy, dephasing is demonstrated to be homogeneous throughout the temperature range studied. Independent measures of T-1 prove that population relaxation contributes negligibly to the dephasing rates. The reduction in temperature gradually leads to a similar to2-fold decrease in the rate of pure dephasing. With cooling the ratio of T-2(n=1)(*)/T-2(n=2)(*) reduces slightly but remains in the range of 2.7 to 2. These results are discussed in terms of Kubo lineshape and Poisson dephasing theories. Neither of these consistently explains the experimental observations assuming reasonable intensities and rates of intermolecular encounters in the solutions. (C) 2003 American Institute of Physics.