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O2(a1Δg) + Mg, Fe, and Ca: experimental kinetics and formulation of a weak collision, multiwell master equation with spin-hopping

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O2(a1Δg) + Mg, Fe, and Ca: experimental kinetics and formulation of a weak collision, multiwell master equation with spin-hopping

dc.contributor.author	Plane, John
dc.contributor.author	Whalley, Charlotte
dc.contributor.author	Francés Soriano, Laura
dc.contributor.author	Goddard, Andrew
dc.contributor.author	Harvey, Jeremy
dc.contributor.author	Glowacki, David
dc.contributor.author	Viggiano, Albert
dc.date.accessioned	2014-10-23T12:20:37Z
dc.date.available	2014-10-23T12:20:37Z
dc.date.issued	2012
dc.identifier.citation	Plane, John Whalley, Charlotte Francés Soriano, Laura Goddard, Andrew Harvey, Jeremy Glowacki, David Viggiano, Albert 2012 O2(a1Δg) + Mg, Fe, and Ca: experimental kinetics and formulation of a weak collision, multiwell master equation with spin-hopping Journal of Chemical Physics 137 1
dc.identifier.uri	http://hdl.handle.net/10550/39318
dc.description.abstract	The first excited electronic state of molecular oxygen, O2(a1Δg), is formed in the upper atmosphere by the photolysis of O3. Its lifetime is over 70 min above 75 km, so that during the day its concentration is about 30 times greater than that of O3. In order to explore its potential reactivity with atmospheric constituents produced by meteoric ablation, the reactions of Mg, Fe, and Ca with O2(a) were studied in a fast flow tube, where the metal atoms were produced either by thermal evaporation (Ca and Mg) or by pulsed laser ablation of a metal target (Fe), and detected by laser induced fluorescence spectroscopy. O2(a) was produced by bubbling a flow of Cl2 through chilled alkaline H2O2, and its absolute concentration determined from its optical emission at 1270 nm (O2(a1Δg<br> X3Σg −). The following results were obtained at 296 K: k(Mg + O2(a) + N2 → MgO2 + N2) = (1.8 ± 0.2) × 10−30 cm6 molecule−2 s−1; k(Fe + O2(a) → FeO + O) = (1.1 ± 0.1) × 10−13 cm3 molecule−1 s<br>1; k(Ca + O2(a) + N2 → CaO2 + N2) = (2.9 ± 0.2) × 10−28 cm6 molecule−2 s−1; and k(Ca + O2(a) → CaO + O) = (2.7 ± 1.0) × 10−12 cm3 molecule−1 s<br>1. The total uncertainty in these rate coefficients, which mostly arises from the systematic uncertainty in the O2(a) concentration, is estimated to be ±40%. Mg + O2(a) occurs exclusively by association on the singlet surface, producing MgO2(1A1), with a pressure dependent rate coefficient. Fe + O2(a), on the other hand, shows pressure independent kinetics. FeO + O is produced with a probability of only ∼0.1%. There is no evidence for an association complex, suggesting that this reaction proceeds mostly by near-resonant electronic energy transfer to Fe(a5F) + O2(X). The reaction of Ca + O2(a) occurs in an intermediate regime with two competing pressure dependent channels: (1) a recombination to produce CaO2(1A1), and (2) a singlet/triplet non-adiabatic hopping channel leading to CaO + O(3P). In order to interpret the Ca + O2(a) results, we utilized density functional theory along with multireference and explicitly correlated CCSD(T)-F12 electronic structure calculations to examine the lowest lying singlet and triplet surfaces. In addition to mapping stationary points, we used a genetic algorithm to locate minimum energy crossing points between the two surfaces. Simulations of the Ca + O2(a) kinetics were then carried out using a combination of both standard and non-adiabatic Rice<br>Ramsperger<br>Kassel<br>Marcus (RRKM) theory implemented within a weak collision, multiwell master equation model. In terms of atmospheric significance, only in the case of Ca does reaction with O2(a) compete with O3 during the daytime between 85 and 110 km.
dc.language.iso	eng
dc.relation.ispartof	Journal of Chemical Physics, 2012, vol. 137, num. 1
dc.subject	Reaccions químiques
dc.subject	Fisicoquímica
dc.title	O2(a1Δg) + Mg, Fe, and Ca: experimental kinetics and formulation of a weak collision, multiwell master equation with spin-hopping
dc.type	journal article	es_ES
dc.date.updated	2014-10-23T12:20:37Z
dc.identifier.doi	10.1063/1.4730423
dc.identifier.idgrec	086261
dc.rights.accessRights	open access	es_ES