RUI: Spectroscopic Characterization and Low Temperature Kinetic Study of Hydrogenated Aromatic Radicals

With support from the Chemical Structure, Dynamics, and Mechanisms A (CSDM-A) program in the Division of Chemistry, Professor Jay Amicangelo of Pennsylvania State University-Erie is investigating the infrared spectra and formation kinetics of hydrogenated radicals produced by the reactions of hydrogen atoms with monosubstituted benzene rings using matrix isolation infrared spectroscopy and computational chemistry. Hydrogenated aromatic radicals are thought to be important intermediates in different chemical processes such as pyrolysis, combustion, hydrogenation, and hydrogenolysis. Complete understanding of the nature of these species as possible intermediates in various important chemical processes remains elusive because of the scarcity of the experimental infrared spectra and formation kinetics data of the hydrogenated radicals at low temperatures. Professor Amicangelo and his students will utilize a microwave discharge source with an appropriate precursor molecule and co-deposit the hydrogen atoms with the ring molecules in argon matrices to obtain the infrared spectra of the hydrogenated radicals and conduct the kinetic studies. Their studies could extend the number of hydrogenated radicals characterized by infrared spectroscopy and provide new low temperature data on their formation kinetics. The Amicangelo research group will also engage in an outreach component to visit high school chemistry classes within the Erie School District with portable scientific devices to help the chemistry teachers give their students access to hands-on, high quality scientific laboratory experiments. This proposal focuses on characterizing the infrared spectra and studying the kinetics of hydrogenated radicals formed by the reaction of hydrogen atoms with monosubstituted benzene rings (C6H5X, X = OCH3, CH3, Cl, CN) using matrix isolation infrared spectroscopy and quantum chemical calculations. Hydrogenated radicals of aromatic rings are thought to be important intermediates in several different important chemical processes, such as pyrolysis, combustion, hydrogenation, and hydrogenolysis. Characterizing the infrared spectra of the hydrogenated radicals will be accomplished by using a microwave discharge source with an appropriate precursor molecule and co-depositing the hydrogen atoms with the ring molecules in 15 K argon matrices. Studying the kinetics of the hydrogenated radicals will involve trapping the hydrogen atoms in the argon matrices at 10 K, followed by monitoring the radical growth kinetics as the hydrogen atoms react with the ring molecules in the argon matrices in the 14 – 20 K temperature range. The IR spectra of these transient intermediates will provide highly valuable windows into the mechanisms of important transformations of aromatic substrates, and as such, will be of broad value to the synthetic, mechanistic and computational chemistry communities. 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.