Tunable VUV pump and tunable VUV probe experiments on the photodissociation dynamics of atmospheric molecules using slice velocity imaging for detection

该奖项由化学结构、动力学和机制项目资助，来自加州大学戴维斯分校的William M. Jackson教授将在190.8 nm到73.8 nm的光谱范围内，对行星大气、彗星和星际介质中重要分子的光化学通道进行表征。最初的研究将用氮、氧、一氧化氮和一氧化碳分子进行。前三种分子对上层大气的化学性质很重要，而最后一种，一氧化碳是星际介质中含量第二丰富的分子，对太阳系的早期发展很重要。基于共振增强四波混频，研制了一种独特的双调谐VUV激光器，其带宽为0.4波数，可调谐范围为190.8 ~ 73.8 nm。其中一种可调谐激光器可用于将分子激发到以分子中的电子、振动和旋转能量为特征的特定能量状态，另一种可用于电离在解离过程中形成的产物原子。这些激光器连接到一个切片成像装置，该装置可以确定产物原子的质量、速度和角分布。这些信息提供了激发态分子的比内能如何影响自旋守恒和产物原子的精细结构分布的关键信息，并为激发态势能曲线的最佳理论计算以及发生在这些曲线上的解离过程提供了关键的测试。氮、氧、一氧化氮和一氧化碳等简单分子只吸收高能太阳光。这种光不能被肉眼看到，也不会在空气中传播。然而，来自太阳的光决定了氮、氧和一氧化氮等分子能在地球和其他行星大气中存在多长时间。它为这些区域发生的化学反应提供能量，也为这个和其他太阳系行星形成初期发生的化学反应提供能量。为了真正了解大气中发生的化学反应，了解这些太阳光线是如何形成反应性原子和碎片的是很重要的。这些反应性物质反过来又与二氧化碳等稳定的微量物质发生化学反应，这些化学反应有助于决定地球上的气候。具有不同能量的太阳光可以从氮和氧分子中生成氮和氧原子，氮和氧分子可以与二氧化碳等微量物质以及氧和氮分子本身发生不同的反应。这项研究将提供关于形成的原子的能量是如何随着吸收的太阳光的能量而变化的信息。这些信息可以被放入模型中，用来预测我们大气层中痕量成分的未来行为，以及其他行星和天体的大气层。

With this award, funded by the Chemical Structure, Dynamics, and Mechanisms - A Program in the Division of Chemistry, Prof. William M. Jackson from the University of California, Davis will characterize the photochemical channels of molecules important in planetary atmospheres, comets, and the interstellar medium in the spectral region between 190.8 and 73.8 nm. The initial studies will be done with the nitrogen, oxygen, nitric oxide, and carbon monoxide molecules. The first three molecules are important for the chemistry of the upper atmosphere, while the last, carbon monoxide is the second most abundant molecule in the interstellar medium and is important in the early development of solar systems. A unique apparatus has been developed with two tunable VUV lasers based on resonance enhanced four wave mixing that has a bandwidth of 0.4 wavenumbers and is tunable between 190.8 and 73.8 nm. One of these tunable lasers can be used to excite the molecule to a particular energy state characterized by the electronic, vibrational, and rotational energy in the molecule and the other can be used to ionize the product atoms that are formed in the dissociation. These lasers are connected to a slice imaging apparatus that can determine the mass as well as the velocity and angular distributions of the product atoms. This information provides critical information about how the specific internal energy of an excited molecule affects the conservation of spin and the fine structure distributions of the product atoms and it provides a critical test for the best theoretical calculations for excited state potential energy curves as well as the dissociation process that occurs on these curves.Simple molecules such as nitrogen, oxygen, nitric oxide, and carbon monoxide only absorb high-energy solar light. This light cannot be seen by the naked eye and it will not travel in air. Yet this light from the sun determines how long molecules such as nitrogen, oxygen and NO can exist in the earth's and other planets atmospheres. It provides the energy for the chemical reactions occurring in these regions as well as those that occurred during the early years of planet formation in this and other solar systems. To truly understand the chemical reactions that do occur in the atmosphere, it is important to understand how this solar light forms the reactive atoms and fragments. These reactive species, in turn, undergo chemical reactions with stable trace species such as carbon dioxide that help determine the climate here on earth. Solar light with different amounts of energy can form nitrogen and oxygen atoms from nitrogen and oxygen molecules that can react differently with both the trace species such as carbon dioxide as well as with the oxygen and nitrogen molecules themselves. The work that will be performed on this grant will provide the information about how the energy of the atoms that is formed changes with the solar energy of the solar light that is absorbed. This information can then be put in the models that are used to predict the future behavior of trace components in our atmosphere as well as the atmospheres of other planets and astronomical bodies.