Infrared emission from the quenching of electronically excited states

当一个分子吸收光形成激发态时，它的总能量增加，它不再与周围环境保持平衡，自然会发生抵消这种平衡的过程，从而恢复平衡。对于电子激发的束缚态（其中吸收在光谱的可见或紫外区域），能量损失的过程可以通过光的发射（荧光）或通过碰撞过程（猝灭）发生。荧光被很好地理解，因为是淬灭率，但什么是远不太了解的是淬灭物种的具体命运-在激发态中包含的（相当大的）能量去了哪里-它是否出现在基态产物的动能或内能，如果化学反应是可能的，什么是产物，它们是用内能形成的？本研究的目的是研究两个重要的气相自由基物种，OH和NO的淬灭的产物。它们将通过吸收紫外光子（分别在308 nm和226 nm处）形成其电子激发态，并通过时间分辨傅里叶变换红外发射（TRFTIRE）技术使用英国独有的设备观察到的产品。第一个要研究的系统将是OH（A）态在与分子氢碰撞中的淬灭。在这里，猝灭的主要结果是水的形成，并且初步结果已经表明，水是热的，具有大量的可用能量以振动的形式出现，并且导致在光谱的中红外区域中的发射。的H2O的发射光谱进行比较，已经获得了这个反应的补充结果，由莱斯特的H原子碎片动能分布的组，和内部的能量分布在OH基态产品的非弹性淬火。我们的理论合作伙伴将对淬火过程进行最先进的计算。其他待研究的系统包括O2、CO和CO2对OH（A）的猝灭，在这些系统中观察到了原子反应产物-我们的研究将通过首次寻找分子反应产物来完成这一过程。对NO（A）态也将进行类似的研究。结果是重要的，在解释激光诱导荧光测量在燃烧系统中，猝灭过程可能导致严重高估的自由基浓度。

When a molecule absorbs light to form an excited state, its total energy increases, it is no longer in equilibrium with its surroundings, and processes will naturally occur to counteract this and thereby restore equilibrium. For an electronically excited bound state (where the absorption is in the visible or ultraviolet region of the spectrum), the process of energy loss can take place through emission of light (fluorescence) or by collisional processes (quenching). Fluorescence is well understood, as are the rates of quenching, but what is far less understood are the specific fates of the quenched species - where does the (considerable) energy contained in the excited state go - does it appear in kinetic or internal energy of the ground state product and if chemical reaction is possible, what are the products and are they formed with internal energy? The purpose of this study is to investigate the products of the quenching of two important gas phase free radical species, OH and NO. They will be formed in their electronically excited states by absorption of ultraviolet photons (at 308 nm and 226 nm respectively), and the products observed by the technique of Time Resolved Fourier Transform InfraRed Emission (TRFTIRE) using an apparatus unique to the UK. The first system to be studied will be the quenching of the OH(A) state in collisions with molecular hydrogen. Here the main result of quenching is the formation of water, and preliminary results have shown that the water is hot, with a great deal of the available energy appearing as vibration, and resulting in emission in the mid-infrared region of the spectrum. The emission spectrum of H2O will be compared with the complementary results already obtained for this reaction by Lester's group on the H atom cofragment kinetic energy distribution, and the internal energy distribution in the OH ground state product of inelastic quenching. State of the art calculations of the quenching processes will be carried out by our theoretical partners. Other systems to be studied include the quenching of OH(A) by O2, CO and CO2, where atomic reaction products have been observed - our studies will complete the picture by looking for the first time at the molecular reaction products. Similar studies on the NO(A) state will also be carried out. The results are of importance in interpreting the laser induced fluorescence measurements in combustion systems, where quenching processes can result in a serious overestimation of the radical concentrations.