title: Kinetic study of the reactions of the sodium dimer (Na2) with a range of atmospheric species.
abstract: The reactions of Na(2) with a series of atmospheric constituents were studied using a fast flow tube with detection of Na(2) by laser induced fluorescence at 656.2 nm [Na(2)(A(1)Sigma(+)(u) - X(1)Sigma(+)(g))]. The resulting rate coefficients at 298 K for the reactions of Na(2) with OH, O(2), NO(2), NO, O(3), H, H(2) and H(2)O are: (1.01(+0.35)(-0.25)) x 10(-10), (2.95 +/- 0.46) x 10(-11), (1.79(+0.51)(-0.31)) x 10(-10), (1.33 +/- 0.16) x 10(-11), (8.0(+24)(-3.0)) x 10(-11), < or =6 x 10(-12), <or =4 x 10(-15), and <or =3 x 10(-13) cm(3) molecule(-1) s(-1), respectively. The quoted uncertainties include measurement imprecision at the 1sigma level, and systematic errors. The reaction between Na(2) and OH produces chemiluminescence at 589 nm [Na(3(2)P(J) - 3(2)S(1/2))], with a measured branching ratio of (7.6(+15.0)(-3.7)) x 10(-3). The reaction enthalpies are calculated using quantum theory at the Complete Basis Set (CBS-Q) level; all reactions except Na(2) + H(2)O and Na(2) + H(2) are exothermic. The surprisingly slow reaction of Na(2) with OH is explained using trajectory calculations and consideration of the splitting between the covalent and ionic surfaces involved in the reaction, coupled with the Landau-Zener formalism. The small upper limit to the rate coefficient for the strongly exothermic reaction Na(2) + H appears to be a striking example of the light atom anomaly where the reaction is kinematically constrained.
authors.affiliation: School of Environmental Sciences, University of East Anglia, Norwich, Norfolk, NR4 7TJ, UK.
authors.forename: Daniel E
authors.initials: DE
authors.lastname: Self
authors.forename: John M C
authors.initials: JM
authors.lastname: Plane
authors.forename: Dwayne E
authors.initials: DE
authors.lastname: Heard
mesh_terms: D003198:Computer Simulation; D006878:Hydroxides / Q000032:analysis* / Q000737:chemistry*; D007700:Kinetics; D008956:Models, Chemical; D008958:Models, Molecular; D012964:Sodium / Q000032:analysis* / Q000737:chemistry*
chemical_list: D006878:Hydroxides; C031356:hydroxide ion; D012964:Sodium