Widely Tunable Cavity-Enhanced Ultrafast Spectroscopy and the Dynamics of Hydrogen Bond Networks

With support from the Chemical Measurement and Imaging Program in the Division of Chemistry, Professor Allison and his research group at Stony Brook University further develop a new type of spectrometer for recording the behavior of gas molecules. In particular, Professor Allison records snapshots of the vibrations of hydrogen bonds between water molecules when a few water molecules stick together in a ring but are otherwise isolated from the environment. These snapshots of simple systems help to understand how the motions of hydrogen atoms in more complex networks such as liquid water are coupled to one another. The information allows scientists to make better computer models of hydrogen-bonded matter. The new ultrafast spectrometers developed by the Allison Lab will be able to record signals from much more dilute samples than currently possible. Professor Allison's techniques, once developed, can be used to study motions of other molecular systems and find many uses in fundamental and applied research. For example, the developed technique could allow scientists to study how water molecules interact with each other to understand how clouds form or to study how protein molecules interact with their surrounding molecules to understand enzymatic functions in biological processes.Professor Allison works with graduate and undergraduate students closely in the research. He also participates in a school summer program on campus targeting high school students. Ultrafast optical spectroscopy methods, such as transient absorption spectroscopy and two-dimensional spectroscopy, are widely used across many disciplines. However, these techniques have been typically restricted to optically thick samples, such as solids and liquid solutions. Professor Allison and his group work on a widely tunable cavity-enhanced ultrafast spectrometer and apply it to the dynamics of elementary hydrogen bond networks. This involves substantial instrument development in concert with a series of experiments on jet-cooled gas-phase molecules and clusters. Cavity-enhanced two-dimensional infrared (CE-2DIR) spectroscopy is another technique to be developed to study hydrogen-bonded carboxylic acid dimers. The study of small deuterated water clusters will provide critical data for understanding and modeling the complexities of liquid water. The development of a widely tunable cavity-enhanced ultrafast spectrometer is expected to open new opportunities for many future applications where classic ultrafast spectroscopy has been limited by its sensitivity and spectral information. The project provides students involved in the project with an interdisciplinary research opportunity. Professor Allison also participates in the University's laser teaching center for the outreach to high school students and general publics.