Oxidation of NO&z.rad; by small oxygen species HO sub(2) super(-) and O sub(2)&z.rad; super(-): the role of negative charge, electronic spin and water solvation

The reactions of HO sub(2) super(-)(H sub(2)O) sub()nand O sub(2)&z.rad; super(-)(H sub(2)O) sub()nclusters (n= 0-4) with NO&z.rad; were studied experimentally using mass spectrometry; the experimental work was supported by quantum chemical computations for the case n= 0, 1. It was found that HO sub(2) super(-)(H sub(2)O) sub()nclusters were efficient in oxidizing NO&z.rad; into NO sub(2) super(-), although the reaction rate decreases rapidly with hydration above n= 1. Superoxide-water clusters did not oxidize NO&z.rad; into NO sub(2) super(-) under the present experimental conditions (low pressure): instead a reaction occurred in which peroxynitrite, ONOO super(-), was formed as a new cluster core ion. The latter reaction was found to need at least one water molecule present on the reactant cluster in order to enable the product to stabilize itself by evaporation of H sub(2)O.