In this project, supported by the Structure, Dynamics and Mechanisms Program of the Chemistry Division, Professor Reisler will undertake a detailed study of the predissociation dynamics of hydrogen-bonded complexes in the gas phase. Despite their weak bonding, hydrogen bonds are crucially important in environments ranging from living cells to icy bodies in the solar system. To gain insight into the predissociation mechanisms, the state resolution and detection sensitivity of photofragment ion imaging will be exploited to obtain pair-correlated distributions of fragments following laser excitation of one subunit of hydrogen-bonded dimers or trimers of water, acids and bases. Cyclic trimers will serve as prototypes of vibrational energy dissipation in larger hydrogen-bonded networks. State-specific energy flow patterns that lead to bond breaking will be inferred from quantum state distributions in the fragments, and bond dissociation energies will be obtained with spectroscopic accuracy. Vibrational predissociation dynamics and mechanisms will be elucidated by comparisons with high-level calculations of benchmark complexes involving water, ammonia, or hydrogen chloride. The ultimate goal is to understand the yet unexplained exquisite state specificity in vibrational energy flow that leads to bond breaking, which depends strongly on the specific complex and the excited vibrational mode.
Students participating in this research observe experimental manifestations of concepts learned in courses on spectroscopy and dynamics, compare their experimental results to theory, and construct dynamical models that emphasize physical insight. The chosen molecular systems are relevant to atmospheric processes that affect climate change, enhancing student awareness of societal impacts. Results will be shared broadly with the scientific community, and the previously developed image reconstruction method, Basis Set Expansion Method (BASEX), continues to be popular. Students learn problem-solving techniques applied to broad areas of science and technology, preparing them to join the high technology workforce. The principal investigator in this project develops and leads a range of activities aimed at encouraging women in science and engineering to pursue research careers. She also participates in mentoring programs that promote career preparation and advancement of members of underrepresented groups.
This project, supported by the Structure, Dynamics and Mechanisms Program of the Chemistry Division, focuses on detailed studies of the binding strength and dissociation dynamics of hydrogen-bonded complexes in the gas phase. Despite its weakness, hydrogen bonding is of crucial importance in environments ranging from our atmosphere to living cells, as well as to icy bodies in our solar system and beyond. Therefore, intense experimental and theoretical effort has been directed towards understanding the making and breaking of hydrogen bonds in the gas and condensed phase. Nevertheless the binding strength of even the most fundamental hydrogen bond, the bond between two water molecules, has not been known with sufficient accuracy to serve as a benchmark for comparison with the most advanced theoretical calculations. The goal of the current study was to gain insight into the formation and breaking of hydrogen bonds by using laser infrared excitation of the complexes, and a sophisticated experimental technique called photofragment ion imaging for fragment detection. These techniques have the required state resolution and detection sensitivity to examine the fragments that are created by breaking the hydrogen bond between two molecules. The major outcome of the work was the first accurate determination of the bond dissociation energy between two water molecules, which was in excellent agreement with the most sophisticated theoretical calculations. In addition, the bond dissociation energies of the dimers of water with a typical acid (hydrogen chloride) and a base (ammonia) were determined with similar high accuracy. Moreover, in collaboration with theory, the mechanism of energy flow in the excited hydrogen-bonded complexes that leads to bond breaking has been elucidated for the first time. The ultimate goal is to understand the yet unexplained exquisite state specificity in vibrational energy flow that leads to bond breaking, which depends strongly on the specific complex and the excited vibrational level. This, in turn, helps understand the weak bonding that governs reactions in solutions and leads to formation of molecular solids of technological importance. The results are transformative to understanding behavior in condensed phases and in molecular solids. Research results are shared with the scientific community through publications and scientific lectures. The previously developed image reconstruction method, Basis Set Expansion Method (BASEX), continues to be supported and shared with scientists around the world. The design and implementation of a novel imaging machine is shared through a website and a publication. Students learn experimental methods and image-reconstruction algorithms that prepare them to join the high technology workforce. The principal investigator has developed and led a broad range of activities aimed at encouraging women in science and engineering to pursue research careers.
