Vibrational substructure in the OH stretching band of water

Spectral diffusion in the OH stretching (νOH) band of water is studied by ultrafast IR-Raman spectroscopy. The νOH transition consists of two overlapping inhomogeneously broadened subbands, a broader (∼500 cm−1) redshifted band and a smaller, narrower (∼200 cm−1) blueshifted band. The blueshifted band, which shows less spectral diffusion, has a longer lifetime (0.75 vs 0.55 ps) and a smaller vibrational frequency blueshift from the ground state (65 vs 90 cm−1), is tentatively assigned to water molecules where one hydrogen atom has a broken hydrogen bond.