Speaker Simon North from Texas A&M University

"Roaming in the Dark: Solving the Complex Atmospheric Photochemistry of the Nitrate Radical" 

 It has been over a century since the nitrate radical, NO₃, was first observed by optical absorption but the mechanism of NO and O₂ production through the visible photolysis has long proven elusive. Recent ion imaging studies and ab initio calculations have suggested that two distinct pathways are responsible for molecular products and that both pathways involve ‘roaming dynamics’ on the ‘dark’ excited electronic state. Thus, the NO₃ → NO + O₂ reaction proceeds in the absence of a traditional transition state.  New detailed measurements, along with ab initio calculations, confirm that both pathways arise from roaming-type mechanisms, but each pathway arises from roaming on a different electronic potential (Science, 355, 1075 (2012)).  This compelling evidence opens additional questions regarding this unusual reaction mechanism including the prevalence of multistate roaming in other molecular systems and the applicability of transition state theory to such systems. 

There will be a reception at 4:30 in the David Love Lounge.