The NO Yield of O(1D) + N2O as Function of Kinetic Energy

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Abstract
The photolysis of pure N2O and of N2O in a large excess of He at 184.9 nm and at 206.2 nm was used as a source of O(1D) atoms, to study the branching ratio of reactions (2a) N2O + O(1D) → N2 + O2 and (2b) N2O + O(1D) → NO + NO, as function of kinetic energy of O(1D). The mole fraction b = k2b/(k2a + k2b) of O(1D) atoms reacting with N2O via (2b) governs the source strength of NO in the stratosphere. The products N2, O2, and NO were measured every 3 minutes by automated gas chromatography, and continuously by a chemi‐luminescence detector as function of time during the photolysis of N2O. Back extrapolation of the product ratios to zero conversion yielded the correct stoichiometry. The value of b derived from initial product ratios was b = 0.617 ± 0.015, independent of kinetic energy in the range 11.3 to 184 kJ/mol. The result is in excellent agreement with a theoretical model of reaction (2) proposed by Tully. The new value of b = 0.617 increases the source strength of NO in the stratosphere by 23% relative to current model calculations based on b = 0.50.

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