Photodissociation Dynamics of Transient Species: Hydrogen-Bonded Dimers and Trimers

University Of Southern California, Los Angeles CA

Investigators

Abstract

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.