Vibrational overtone excitation in electron mediated energy transfer at metal surfaces
Vibrational overtone excitation in electron mediated energy transfer at metal surfaces
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金属表面电子介导能量转移的振动泛音激发
DOI：
10.1039/c0sc00141d
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发表时间：
2010
期刊：
影响因子：
8.4
通讯作者：
A. Wodtke
中科院分区：
文献类型：
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作者：
R. Cooper;I. Rahinov;D. Matsiev;D. Auerbach;A. Wodtke
一般来说，光子激发振动泛音是无效的，但在某些情况下，电子可以有效地激发振动泛音。在这里，我们证明了电子介导的振动泛音激发分子碰撞与金属表面。具体来说，我们报告了NO（ν = 0）与Au（111）表面碰撞时ν = 1和ν = 2的绝对振动激发概率是表面温度从300到985 K的函数。在所有情况下，观察到的振动激发NO的居群都接近于与表面完全热化的居群，尽管事实上散射是通过亚ps持续时间的直接“单弹跳”机制发生的。我们提出了一个状态到状态的动力学模型，该模型准确地描述了接近完全热化的情况（我们称之为强耦合情况），并使用该模型提取状态到状态的速率常数。这一分析明确地表明，直接振动泛音激发主导了ν = 2的产生，并且在我们的模型中，泛音跃迁的内在强度与单量子跃迁的量级相同，这表明了一种可能的方法来绕过分子振动泵浦中的光学选择规则。这一结果还表明，先前测量的高振动激发NO的振动弛豫表现出高效的多量子跳变（Δν ~−8），在机制上与NO（ν = 0）的振动激发相似。
Vibrational overtone excitation is, in general, inefficiently stimulated by photons, but can under some circumstances be efficiently stimulated by electrons. Here, we demonstrate electron mediated vibrational overtone excitation in molecular collisions with a metal surface. Specifically, we report absolute vibrational excitation probabilities to ν = 1 and 2 for collisions of NO(ν = 0) with a Au(111) surface as a function of surface temperature from 300 to 985 K. In all cases, the observed populations of vibrationally excited NO are near those expected for complete thermalization with the surface, despite the fact that the scattering occurs through a direct “single bounce” mechanism of sub-ps duration. We present a state-to-state kinetic model, which accurately describes the case of near complete thermalization (a regime we call the strong coupling case) and use this model to extract state-to-state rate constants. This analysis unambiguously shows that direct vibrational overtone excitation dominates the production of ν = 2 and that, within the context of our model, the intrinsic strength of the overtone transition is of the same order as the single quantum transition, suggesting a possible way to circumvent optical selection rules in vibrational pumping of molecules. This result also suggests that previous measurements of vibrational relaxation of highly vibrationally excited NO exhibiting highly efficient multi-quantum jumps (Δν ∼ −8) are mechanistically similar to vibrational excitation of NO(ν = 0).