Ultrafast memory loss and energy redistribution in the hydrogen bond network of liquid water

Using two-dimensional infrared spectroscopy, this work has dissected the intermolecular dynamics in the fully resonant hydrogen-bonded network of liquid H₂0. This work involved the development of new infrared laser sources with sufficient (µJ) pulse energies, as well an experimental apparatus suitable for performing phase sensitive infrared (IR) spectroscopy. In particular, the development of a diffractive optics based experimental setup for use in the IR, as well as nanofluidics for handling the strong absorption of pure H₂0, were found to be necessary for extracting the relevant water dynamics, and are described in detail. Resonant energy transfer on a 100 fs time scale is observed in H₂0, as well as extremely fast spectral diffusion that results in a spectral sweep in the OH frequencies on a 50 fs time scale. There is an equally fast dephasing process observed in the system, leading to a near complete loss of inhomogeneity within 50 fs. The net effect is a very efficient redistribution of energy in liquid water. These results are in dramatic contrast to studies of isotopic water and clearly illustrate the importance of studying pure liquid H₂0 directly. These findings lead to new appreciation of the significance of fully resonant conditions for energy exchange and coupling among different degrees of freedom that can only be probed for pure H₂0.Ph.D