The Hansen Group’s research objective is to improve the understanding of atmospheric chemistry processes through focused laboratory and computational studies. The oxidizing, or cleansing efficiency of the atmosphere is generally defined by the concentration of HO_x (HO_x = [OH] and [HO₂]). Photochemical models utilize reaction rate coefficients for reactions involving HO_x species to predict lifetimes and product formation from the oxidation of atmospheric pollutants. Recent work has highlighted the importance of HO₂-moleucle complexes on increasing the reactivity of HO₂ radical. Our group uses a combination of computational and experimental techniques to probe both the kinetics and spectroscopy of radical-molecule complexes. Experimental work on the kinetics of the HO₂ self-reaction indicates that the reaction mechanism proceeds through an HO₂-CH₃OH complex, when CH₃OH is used as the HO₂ precursor. The HO₂ self-reaction rate has been shown to increase by as much as a factor of two under conditions when the complex is formed. Shown here is the minimum energy structure of an HO₂-CH₃OH complex identified using high level ab initio calculations.

Our group studies the spectroscopy and kinetics of radical-molecule formation using a variety of techniques such as nano-second step-scan FTIR, matrix isolation spectroscopy, UV time-resolved spectroscopy and wavelength modulated diode laser spectroscopy.

The results of our studies are incorporated into existing photochemical models in an effort to increase their predictive an interpretive powers.