Both IR and anti-Stokes Raman measurements on OH stretch vibrations νOH of water see two time constants, ∼0.3 and ∼0.6 ps. We attribute the former to spectral diffusion and the latter to the ν OH lifetime. This interpretation is evident from our Raman spectra, which show the νOH spectrum changing shape and the ν OH population decaying. The νOH decay is accompanied by the rise (∼0.6 ps) and subsequent fall (∼1.4 ps) of population in the δOH bending vibration. Bakker et al. [Chem. Phys. Lett. 385 (2004) 329] assert their IR data indicates an absence of (>100 fs) spectral diffusion, that the faster time constant is the νOH lifetime and that the slower is the lifetime of a conjectured intermediate state. The properties of this conjectured intermediate differ significantly from the bending vibration directly observed by us. The intensity analysis by Bakker et al. said to contradict our interpretation relies entirely on ad hoc assumptions about excited-state absorptions. We show these ad hoc assumptions are unfounded and some are unreasonable, and that a plausible explanation for the IR intensities exists that is consistent with our interpretation.
ASJC Scopus subject areas
- Physics and Astronomy(all)
- Physical and Theoretical Chemistry