Mechanistic Inside into the Gas-Phase NO3·+HO2· Reaction

The reaction between <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msubsup><mml:mi>NO</mml:mi><mml:mn>3</mml:mn><mml:mo>·</mml:mo></mml:msubsup></mml:math> and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msubsup><mml:mrow><mml:mi>HO</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow><mml:mrow><mml:mo>·</mml:mo></mml:mrow></mml:msubsup></mml:math> is critical in nighttime atmospheric chemistry. This reaction is believed to occur via two channels: one leading to the formation of HNO₃ and the other forming <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msup><mml:mrow><mml:mi>OH</mml:mi></mml:mrow><mml:mrow><mml:mo>·</mml:mo></mml:mrow></mml:msup></mml:math>. A long-standing question regarding this reaction is whether this reaction occurs through HNO₃ path or <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msup><mml:mrow><mml:mi>OH</mml:mi></mml:mrow><mml:mrow><mml:mo>·</mml:mo></mml:mrow></mml:msup></mml:math> or both at a time. Some indirect experiments proposed the HNO₃ path as the exclusive path, while some suggested the possibility of both the paths. In the present work, using high-level quantum chemical and kinetics calculations, we have tried to shed light on the mechanism of this reaction. We have incorporated full triple excitation and partial quadratic excitation corrections at the coupled-cluster level for our energetics part, whereas a master equation approach has been employed to obtain the rate constants within 213-400 K. Our investigation suggests that it is only the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msup><mml:mrow><mml:mi>OH</mml:mi></mml:mrow><mml:mrow><mml:mo>·</mml:mo></mml:mrow></mml:msup></mml:math> path through which the reaction takes place.