화학공학소재연구정보센터
Journal of Physical Chemistry A, Vol.109, No.40, 9035-9043, 2005
Especially significant new component of N2O quantum yield in the UV photolysis of O-3 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 O-3 in air, from Estupinan 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 O-3, tentatively O-3(B-3(1)), 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 [O-3] in the photolyzed O-3/air mixture. Further experiments with [O-3] 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 O-3 would also help.