JILA, National Institute of Standards and Technology, Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado 80309-0440, USA.
Faraday Discuss. 2011;150:471-9; discussion 505-32. doi: 10.1039/c0fd00023j.
The dynamics of HCI scattering from a room-temperature -CH3 terminated self-assembled monolayer (SAM) is probed via state-resolved spectroscopy coupled to a velocity-map imaging (VMI) apparatus. The resulting velocity maps provide new insight into the HCl scattering trajectories, revealing for the first time correlations between internal and translational degrees of freedom. Velocity maps at low J are dominated by signatures of both the incident beam (17.3(3) kcal mol(-1)) and a room-temperature trapping-desorption component (TD). At high J, however, the maps contain a large, continuous feature associated primarily with impulsive scattering (IS). Trajectories resulting from these strongly inelastic interactions are readily isolated in the map, and provide a new glimpse into purely impulsive scattering dynamics. Specifically, within the purely-IS HCI region of the velocity maps, the rotational distribution is found to be remarkably Boltzmann like, but with a temperature (472 K) significantly higher than the SAM surface (300 K). By way of contrast, the translational degree of freedom of the impulsively-scattered flux is clearly non-Boltzmann in character, with a strong propensity for in-plane scattering in the forward direction, and yet still exhibiting out-of-plane velocity distributions reasonably well characterized by a temperature of 690 K. These first data establish the prospects for a new class of experimental tools aimed at exploring energy transfer and reactive scattering events on SAMs, liquid, and metal interfaces with quantum state resolved information on correlated internal and translational distributions.
通过与速度映射成像（VMI）仪器耦合的状态分辨光谱，研究了室温-CH3 终止自组装单层（SAM）中 HCI 散射的动力学。所得速度图提供了对 HCl 散射轨迹的新见解，首次揭示了内部和平移自由度之间的相关性。低 J 时的速度图主要由入射束（17.3(3) kcal mol(-1))和室温捕获-解吸成分（TD）的特征来主导。然而，在高 J 时，地图包含与脉冲散射（IS）主要相关的大连续特征。这些强烈非弹性相互作用产生的轨迹很容易在地图中分离出来，并为纯粹的脉冲散射动力学提供了新的见解。具体而言，在速度图的纯粹 IS HCI 区域中，发现旋转分布非常类似于玻尔兹曼分布，但温度（472 K）明显高于 SAM 表面（300 K）。相比之下，脉冲散射通量的平移自由度的特征明显是非玻尔兹曼的，在向前方向上具有强烈的平面内散射倾向，但仍然表现出与平面外速度分布相当吻合的特征，其温度为 690 K。这些第一组数据为一类新的实验工具开辟了前景，这些工具旨在探索 SAM、液体和金属界面上的能量转移和反应散射事件，同时具有关于相关内部和平移分布的量子态分辨信息。
