Hydrogen Bond Rearrangements in Water Probed with Temperature-Dependent 2D IR

Abstract

We use temperature-dependent two-dimensional infrared spectroscopy (2D IR) of dilute HOD in H2O to investigate hydrogen bond rearrangements in water. The OD stretching frequency is sensitive to its environment, and loss of frequency correlation provides a picture of local and collective hydrogen bond dynamics. The time scales for hydrogen bond rearrangements decrease from roughly 2 ps at 278 K to 0.5 ps at 345 K. We find the barrier to dephasing and hydrogen bond switching to be Ea = 3.4 ± 0.5 kcal/mol, although the trend is slightly non-Arrhenius. The value is in good agreement with the reported barrier height for OD reorientation observed in pump−probe anisotropy measurements. This provides evidence for the proposal that hydrogen bond switching occurs through concerted large angular jump reorientation. MD simulations of temperature-dependent OD vibrational dephasing and orientational correlation functions are used to support our conclusions.