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首页> 美国卫生研究院文献>Proceedings of the National Academy of Sciences of the United States of America >On the strong and selective isotope effect in the UV excitation of N2 with implications toward the nebula and Martian atmosphere
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On the strong and selective isotope effect in the UV excitation of N2 with implications toward the nebula and Martian atmosphere

机译：关于N2的紫外线激发中的强选择性同位素效应对星云和火星大气有影响

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摘要

Isotopic effects associated with molecular absorption are discussed with reference to natural phenomena including early solar system processes, Titan and terrestrial atmospheric chemistry, and Martian atmospheric evolution. Quantification of the physicochemical aspects of the excitation and dissociation processes may lead to enhanced understanding of these environments. Here we examine a physical basis for an additional isotope effect during photolysis of molecular nitrogen due to the coupling of valence and Rydberg excited states. The origin of this isotope effect is shown to be the coupling of diabatic electronic states of different bonding nature that occurs after the excitation of these states. This coupling is characteristic of energy regimes where two or more excited states are nearly crossing or osculating. A signature of the resultant isotope effect is a window of rapid variation in the otherwise smooth distribution of oscillator strengths vs. frequency. The reference for the discussion is the numerical solution of the time dependent Schrödinger equation for both the electronic and nuclear modes with the light field included as part of the Hamiltonian. Pumping is to all extreme UV dipole-allowed, valence and Rydberg, excited states of N2. The computed absorption spectra are convoluted with the solar spectrum to demonstrate the importance of including this isotope effect in planetary, interstellar molecular cloud, and nebular photochemical models. It is suggested that accidental resonance with strong discrete lines in the solar spectrum such as the CIII line at 97.703 nm can also have a marked effect.
机译：结合自然现象讨论了与分子吸收有关的同位素效应，这些自然现象包括早期的太阳系过程，土卫六和地球大气化学以及火星大气演化。激发和离解过程的物理化学方面的量化可能会导致人们对这些环境的了解加深。在这里，我们研究由于价态和里德堡激发态的耦合而在分子氮的光解过程中产生额外同位素效应的物理基础。同位素效应的起因是激发这些态后发生的，具有不同键合性质的非绝热电子态的耦合。这种耦合是两个或多个激发态几乎交叉或振荡的能量状态的特征。所产生的同位素效应的标志是振荡器强度与频率的平稳分布迅速变化的窗口。讨论的参考是电子和核模态与时间相关的Schrödinger方程的数值解，其中光场是哈密顿量的一部分。泵浦是所有允许的极端紫外线偶极子，价态和里德堡N2激发态。计算得出的吸收光谱与太阳光谱有卷积关系，以证明将这种同位素效应包括在行星，星际分子云和星云光化学模型中的重要性。建议与太阳光谱中强离散线（例如97.703 nm处的CIII线）发生意外共振也会产生显着影响。

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