Products of the quenching of NO A 2Σ+ (v = 0) by N2O and CO2

Abstract

Collisional quenching of NO A ²Σ⁺ (v = 0) by N₂O and CO₂ has been studied through measurements of vibrationally excited products by time resolved Fourier transform infrared emission. In both cases vibrationally excited NO X ²Π (v) is seen and quantified in levels v ≥ 2 with distributions which are close to statistical. However the quantum yields to produce these levels are markedly different for the two quenchers. For CO₂ such quenching accounts for only ca. 26% of the total: for N₂O it is ca. 85%. Far more energy is seen in the internal modes of the CO₂ product than those of N₂O. The results are rationalised in terms of cleavage of the N₂–O bond being dominant in the latter case, with either a similar O atom production or a specific channel producing almost exclusively NO in low vibrational levels (v = 0,1) for quenching by CO₂. Minor reactive channels yielding NO₂ are seen in both cases, and O(¹D) is observed with low quantum yield in the reaction with N₂O. The results are discussed in terms of previous models of the quenching processes, and are consistent with the very high yield of NO X ²Π (v = 0) previously observed by laser induced fluorescence for quenching of NO A ²Σ⁺ (v = 0) by CO₂.