Vibrational Dynamics in Water From the Molecule's Perspective

Liquid water is a fascinating substance, ubiquitous in chemistry, physics, and biology. Its remarkable physical and chemical properties stem from the intricate network of hydrogen bonds that connect molecular participants. The structures and energetics of the network can explain the physical properties of the substance on macroscopic length scales, but the events that initiate many chemical reactions in water occur on the time scales of 0.1- 1 picosecond. The experimental challenges of measuring specific molecular motions on this time scale are formidable. The absorption frequency of the OH stretch of HOD in liquid D20 is sensitive to the hydrogen bonding and molecular environment of the liquid. Ultrafast IR experi-ments endeavor to measure fluctuations in the hydrogen bond network by measuring spectral fluctuations on femtosecond time scales, but the data do not easily lend themselves to a direct microscopic interpretation. Computer simulations of empirical models, however, offer explicit microscopic detail but must be adapted to include a quantum mechanical vibration. I have developed methods in computer simulation t