Laboratory Studies of Atmospherically Important Gas- Phase Peroxy Radical Reactions

摘要: Peroxy radicals (HO2, RO2) are important intermediates in Earth's atmosphere. They the oxidation of alkanes and CO combustion atmospheric chemical processes. In earth's atmosphere, rates their self cross reactions often dominant loss processes when NOx concentrations fall below tens pptv. These have proven difficult to study laboratory experiments, due complex secondary chemistry ambiguities radical detection. This thesis describes a new laser-photolysis apparatus measure peroxy under conditions that employs simultaneous UV direct absorption IR wavelength-modulation spectroscopy detect radicals. Prior kinetic measurements gas-phase typically employed flash-photolysis methods coupled with detection only by spectroscopy. However, uncertainties can arise because several different species contribute signal. The channel provides an independent means monitoring HO2 specific rovibrational transitions. With this apparatus, + NO2, CH3O2, CH3O2 were studied at temperatures from 219 K 300 K. Our have, some cases, led significant revision previously accepted rate constants, mechanisms, or product yields, especially relevant upper coefficients for reaction shown account long-standing discrepancy modeled vs. observed hydrogen peroxide stratosphere. A key finding has been observation many previous low suffered problems complexation between methanol, precursor used generate HO2. Direct evidence is presented formation HO2?CH3OH complex; coefficients, equilibrium constant, enthalpy CH3OH measured. results first chaperone effect proposed explain enhancement self-reaction hydrogen-bonding species. The effects methanol on For NO2 reaction, overlapping, time-dependent signals N2O4 may not properly accounted measurements. Other studies conducted 250 be subject similar errors. products raised questions concerning yields mechanisms.