Reactivity of NO with anionic water clusters A(-)center dot(X(2)O)(n) (A=O, OX, O-2, and XO(2); X=D and H). Formation of (NO)(2) and N2O3 and their reactions

The reactivity of NO toward anionic water clusters, A(-).(X(2)O)(n), A = O, OX, O-2, and XO(2); X = D and H), at several temperatures within the range 157-298 K, and at helium buffer gas pressures between 0.28 and 0.43 Turr, was studied using a flow-tube apparatus. The O-.(X(2)O)(n less than or equal to 5) and O-2(-).(X(2)O)(n less than or equal to 3) clusters were observed to react guile efficiently with NO, and the rate constants for these reactions were determined. The observed rate constants for O-2(-).(X(2)O)(n), show a positive temperature dependence. This observation is explained in terms of an energy barrier to the isomerization of the peroxy structural form, ONOO-.(X(2)O)(n), to the conventional nitrate anion structure, NO3-.(X(2)O)(n). For OX(-).(X(2)O)(n less than or equal to 5), no detectable reaction with NO was observed to occur. Evidence for formation of the NO dimer and N2O3 in the flow-tube apparatus is presented. Under the flow-tube conditions employed, the N2O3 species is found to react efficiently with OX(-).(X(2)O)(n less than or equal to 5), XO(2)(-).(X(2)O)(n less than or equal to 4) and NO2-.(X(2)O)(n less than or equal to 2) via a ligand switching mechanism. The implications of these studies for atmospheric anal environmental chemistry are briefly discussed.