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，它不再与周围环境处于平衡状态，并且自然会发生过程来抵消这一点，从而恢复平衡。对于电子激发态（吸收在光谱的可见或紫外区域），能量损失的过程可以通过发光（荧光）或碰撞过程（猝灭）发生。人们对荧光和猝灭速率都很了解，但人们对猝灭物质的具体命运却知之甚少——激发态中包含的（相当大的）能量去了哪里？它是出现在基态产物的动能中还是内能中？如果可能发生化学反应，产物是什么？它们是用内能形成的吗？本研究的目的是研究两种重要的气相自由基OH和NO的猝灭产物。它们将通过吸收紫外光子（分别为308 nm和226 nm）在电子激发态下形成，并使用英国独有的设备通过时间分辨傅立叶变换红外发射技术（TRFTIRE）观察产物。要研究的第一个系统将是OH(A)态在与氢分子碰撞时的猝灭。这里淬火的主要结果是水的形成，初步结果表明，水是热的，大量的可用能量表现为振动，并在光谱的中红外区域产生发射。将H2O的发射光谱与Lester's基团已经得到的该反应的互补结果在H原子共碎片动能分布和非弹性猝灭OH基态产物的内能分布上进行比较。淬火过程的最先进的计算将由我们的理论合作伙伴进行。其他有待研究的体系包括O2、CO和CO2对OH(A)的猝灭，在这些体系中已经观察到原子反应产物——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)状态的类似研究也将进行。该结果对于解释燃烧系统中激光诱导荧光测量具有重要意义，在燃烧系统中，猝灭过程可能导致自由基浓度的严重高估。

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.