Chemistry of Singlet Oxygen [O2(a1DELTAg)] in the Upper Atmosphere
Abstract
This project completed the following objectives: - developed a method (based on technique pioneered by Dr A. Viggiano) to produce molecular oxygen in it's first electronically excited state; - produced an absolute calibration of the O2(a) concentration which showed the yield of O2(a) from the Cl2 generator ranged from 16 to 26%; - studied the reaction kinetics at 300 K of atomic Mg, Ca and Fe with O2(a) in a fast flow tube, where the metal atoms were produced either by thermal evaporation (Mg and Ca) or pulsed laser ablation (Fe), and then detected by laser induced fluorescence; - carried out high level electronic structure calculations to explore the potential energy surfaces for these metal atom + O2(a) reactions, as well as the reaction SiO + O2(a); Conclusions include: - the reaction Ca + O2(a) mostly occurs via recombination to produce CaO2(1A1), with a rate coefficient that is ~80 times larger than for the reaction Ca + O2(X). There is also limited switching through a conical intersection between singlet and triplet surfaces, leading to the bimolecular products CaO + O; - the reaction Mg + O2(a) occurs exclusively by recombination on a singlet surface, producing MgO2(1A1). The rate coefficient is ~4000 times larger than for the reaction Mg + O2(X). However, there are no surface crossings between the initial singlet and lower-lying triplet surfaces; - the reaction Fe + O2(a) produces FeO + O, although with a probability of only ~ 0.1%. There is no evidence for recombination, suggesting that this reaction proceeds mostly by near-resonant electronic energy transfer, producing O2(X) and Fe(a5F) (the lowest-lying excited state of Fe); - the reaction SiO + O2(a) has a significant barrier of 55 kJ mol-1 and also requires a singlet-triplet surface crossing in order to produce SiO2 + O; - the reaction Si(cation) + O2(a) is the most important removal process for Si cations in the daytime atmosphere between 85 and 107 km.
Document Details
- Document Type
- Technical Report
- Publication Date
- Feb 06, 2012
- Accession Number
- ADA562330
Entities
People
- John M. Plane
Organizations
- University of Leeds