Figure 5.

Schematic of vibrational energy relaxation. Near-resonant vibrational Förster energy transfer between different O–H (or in this case O–D) groups with slightly different frequencies gives rise to spectral diffusion within the inhomogeneously broadened absorption band. The rate of energy transfer is given by the spectral overlap (pink areas). The bend overtone spectrum is shown schematically in purple below. For OD groups that overlap spectrally with the bend overtone (purple areas), coupling to that bend overtone allows for vibrational relaxation to occur. Reprinted with permission from ref (81). Copyright 2016 American Chemical Society.