Event

Title: “Autoxidation chemistry driven by isomerizations:  the direct observation of a hydroperoxy alkyl radical"

Complex-forming reactions have at least one deep well on their potential energy surface, where the well represents a reactive intermediate on the pathway to products.  Just as in direct reactions, where the observation of a transition state complex provides important clues to the reaction mechanism, the characterization of reactive intermediates is enormously useful in discovering the mechanism of complex-forming reactions.  However, most reactive intermediates are short-lived, elusive molecules that are difficult to catch and challenging to detect. 

In atmospheric chemistry, the oxidation of volatile organic compounds adds oxygen atoms to hydrocarbons, thereby lowering their volatility, leading to formation of secondary organic aerosols (SOA).  Models predicting the growth of SOA do not achieve the rates of growth seen in atmospheric measurements.  This discrepancy may mean that an important chemical mechanism is missing from the models.  Our understanding of both autoignition chemistry and autooxidation in the atmosphere is incomplete partly because a key reactive intermediate known to be important in these mechanisms, hydroperoxyalkyl radicals (denoted ·QOOH), has never been directly detected until now.  We have measured the production and consumption kinetics of a ·QOOH radical, and measured its photoionization spectrum to confirm its identity.  In this talk, I will discuss why such measurements are important for making models of combustion and atmospheric chemistry more predictive, and present our experiments, theory, and modelling that led to this discovery. 

Inquires please contact Rosa M. Vargas rvargas@sas.upenn.edu