Figure 2.

Experimentally observed IVR decays obtained by McDonald and coworkers (16, 17), fitted to exponential and power law models given in the text. The log–log plots clearly become linear with small quantum beats at long times, before eventually settling to a constant average value. The exponential function provides a good fit only at short times where I(t) ≥ 1/e. The Bottom also shows a biexponential fit, which provided a reasonable representation of the cyclohexylaniline data due to the low coefficient of the power law. However, in all cases χ² of the fit was a least a factor of 1.8 better with the two-parameter power law model than with the three-parameter biexponential.