Especially significant new component of N2O quantum yield in the UV photolysis of O3 in air.
This paper presents an alternate three-component model for the density ([M]) and temperature (T) dependence of the N2O quantum yields (phi(N2O), in the UV photolysis of O3 in air, from Estupiñán et al.'s (ENLCW's) high-quality experiments that were a breakthrough in the pressure and T coverage. The three components consist of a new [M]-independent component, the ENLCW-discovered [M]1 component, and the [M]2-dependent component found by Kajimoto and Cvetanovic. The [M]1 component is T independent. The weak T dependence of ENLCW's phi(N2O) results from the T dependence of the other two components. The agreement of the three-component model with the observed phi(N2O) is much better than that of ENLCW's one-component (T-dependent linear-in-[M]) model. For example, the percentage residual for a significant two-thirds of all data is better than +/-8% in the three-component model compared to only one-third for the ENLCW model. The improvements due to the three-component model are real in the sense that they are obvious despite the experimental error bars in that pressure-temperature domain where the reality is expected to reveal itself in the ENLCW experiment. Also, the new [M]-independent component is nonzero positive at a very high confidence level of 97.5%, sharply contrasting with the current perception. The [M]-independent component is especially significant despite being small compared to the dominant [M]1 component. It implies N2O formation from excited O3, tentatively O3(3B1), immune from ENLCW and Prasad controversy over the origin of the [M]1 component. In the suggested interpretation, the [M]0 component varies linearly with [O3] in the photolyzed O3/air mixture. Further experiments with [O3] fixed at various amounts, while the air density and temperature are varied, could check the interpretation. Further computational-chemistry studies to better characterize the low-lying triplet states of O3 would also help.
Prasad
Sheo S
SS
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