SCHEDULED MAINTENANCE
Low temperature reaction of chlorine nitrate with water ice Formation of molecular nitric acid
Abstract
We have examined the reaction of ClONO2 with water ice at 140 K and found evidence for the formation of molecular nitric acid under conditions of reduced surface water. This is very different from the behaviour of ClONO2 on ice at 180 K, where substrate-induced pre-reaction ionisation of ClONO2 leads to a reaction mechanism involving the intermediacy of [H2OCl]+ and nitrate ions. These two results are not inconsistent with a single mechanism if a subtle change in the interplay between the availability of water molecules at the surface and the variation of the substrate/adsorbate interactions of ice/ClONO2 with temperature are taken into account. This implies that reaction mechanisms and product branching ratios in the atmosphere may vary widely over a range of temperatures and reactant partial pressures.
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