Kinetics of the Gas Phase Reaction Between Nitric Oxide, Nitrogen Dioxide and Water Vapor

Using the absorption of light by nitrogen dioxide as a measure of its concentration, the rate of the reaction NO2 + NO + H2O(g) = 2HNO2O(g) has been measured over a five-fold range of water vapor and nitrogen dioxide concentrations, with nitric oxide greatly in excess. Changes in light intensity were detected by means of an electron-multiplier phototube and recorded by photographing the screen of cathode-ray oscilloscope. Half-times as short as 0.014 sec. were observed. The reaction rate was found to depend more strongly upon the concentration of water vapor than upon that of nitrogen dioxide and to be kinetically consistent with a mechanism involving termolecular collisions. An incidental results of the study, the equilibrium constant of the above reaction has been calculated and its order of magnitude experimentally confirmed, and a lower limit has been fixed for the rate of dissociation of nitrogen sesquioxide.