Untangling the Energetics and Dynamics of Elementary Reactions of Silylidyne (SiH) Radicals and their Role in the Gas Phase Formation of Exotic Silicon Heterocycles

Professor Ralf I. Kaiser at the University of Hawaii is investigating experimentally the reactions of the simplest silicon-containing radicals silylidyne with key classes of cyclic hydrocarbons along with their nitrogen-substituted counterparts to unravel the chemical dynamics involved in the formation of bicyclic silicon-bearing molecules in the gas phase. These experiments are exceptionally challenging considering the sensitivity of organosilicon species to air, short lifetimes, and the tendency to form dimers thus classifying (bi)cyclic organosilicon species as one of the least explored classes of organosilicon molecules. Professor Kaiser and his students will unravel the energy-dependent chemical dynamics of bimolecular reactions under single collision conditions utilizing an ultra-clean crossed molecular beam setup equipped with an angular resolved time-of-flight mass spectrometer detector, hard and soft electron impact ionization, and laser induced fluorescence detection. The experimental results will be integrated with ab initio and quasi classical trajectory calculations to provide basic insights on the chemical dynamics of reactive systems forming silicon heterocyclic organic molecules. These studies will advance the fundamental understanding of chemical bonding, reactivity, and electronic structure of silicon-bearing molecules, and their role in the chemistry of the interstellar medium. This project will integrate research along with training and outreach activities through organization of an interdisciplinary symposium “200 Years Silicon–Celebrating New Directions of Silicon Chemistry” at the American Chemical Society (ACS) Meeting, broadening the participation of undergraduate students in hands-on research on reaction dynamics, and expanding public awareness by relaying the latest breakthroughs from the research to high school students. This study will systematically conduct state-of-the-art crossed molecular beam experiments of the simplest open-shell silicon radical (silylidyne) with prototype cyclic, unsaturated hydrocarbons carrying main group elements across the second row. By integrating these experiments with ab initio and quasi-classical trajectory (QCT) calculations in collaboration with Prof. Rui Sun, the project will provide a comprehensive understanding of the chemical dynamics of silicon-containing systems. These investigations will deliver basic insights on: i) the previously elusive reaction pathways and chemical dynamics of reactive systems forming silicon heterocyclic organic molecules, many of which have been only theoretically predicted, ii) predictive concepts for nonadiabatic and excited-state dynamics in silicon-containing systems, including energy transfer, isomerization, intersystem crossing, spin-orbit coupling, and heavy-atom effects, iii) fundamental principles of chemical bonding in silicon-based molecules, iv) the unimolecular decomposition of chemically activated silicon-bearing reactive intermediates and the factors controlling their reactivity (internal energies, electronic states), and v) novel reaction mechanisms unique to silicon-bearing species that have no analog in isovalent carbon molecules. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria. NSF Award ID: 2538802 | Program: 01002627DB NSF RESEARCH & RELATED ACTIVIT | Principal Investigator: Ralf Kaiser | Institution: University of Hawaii, HONOLULU, HI | Award Amount: $470,000 View on NSF Award Search: https://www.nsf.gov/awardsearch/show-award/?AWD_ID=2538802 View on Research.gov: https://www.research.gov/awardapi-service/v1/awards/2538802.html