JILA, University of Colorado and National Institute of Standards and Technology, and Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado 80309-0440, USA.
Phys Chem Chem Phys. 2012 Mar 28;14(12):4070-80. doi: 10.1039/c1cp22938a. Epub 2011 Dec 9.
This work describes a novel surface-scattering technique which combines resonance enhanced multiphoton ionization (REMPI) with velocity-map imaging (VMI) to yield quantum-state and 2D velocity component resolved distributions in the scattered molecular flux. As an initial test system, we explore hyperthermal scattering (E(inc) = 21(5) kcal mol(-1)) of jet cooled HCl from Au(111) on atomically flat mica surfaces at 500 K. The resulting images reveal 2D (v(in-plane) and v(out-of-plane)) velocity distributions dominated by two primary features: trapping/thermal-desorption (TD) and a hyperthermal, impulsively scattering (IS) distribution. In particular, the IS component is strongly forward scattered and largely resolved in the velocity map images, which allows us to probe correlations between rotational and translational degrees of freedom in the IS flux without any model dependent deconvolution from the TD fraction. These correlations reveal that HCl molecules which have undergone a large decrease in velocity parallel to scattering plane have actually gained the most rotational energy, reminiscent of a dynamical energy constraint between these two degrees of freedom. The data are reduced to a rotational energy map that correlates <E(rot)> with velocity along and normal to the scattering plane, revealing that exchange occurs primarily between rotation and the in-plane kinetic energy component, with v(out-of-plane) playing a relatively minor role.
这项工作描述了一种新颖的表面散射技术，该技术将共振增强多光子电离（REMPI）与速度映射成像（VMI）相结合，以在散射分子流中产生量子态和二维速度分量分辨分布。作为初始测试系统，我们研究了在 500K 下，从 Au(111)喷射冷却的 HCl 对原子级平坦云母表面的超热散射（E(inc) = 21(5) kcal mol(-1)）。所得图像显示二维（v(in-plane)和 v(out-of-plane））速度分布主要由两个主要特征主导：捕获/热解吸（TD）和超热、脉冲散射（IS）分布。特别是，IS 成分强烈向前散射，在速度映射图像中得到了很大程度的分辨，这使我们能够在不依赖于 TD 分数的任何模型反卷积的情况下，探测 IS 通量中旋转和平移自由度之间的相关性。这些相关性表明，与散射平面平行的速度大幅降低的 HCl 分子实际上获得了最大的旋转能量，这让人联想到这两个自由度之间的动态能量约束。数据被简化为一个旋转能量图，该图将<E(rot)>与沿和垂直于散射平面的速度相关联，揭示了主要发生在旋转和平面内动能分量之间的交换，而 v(out-of-plane)则起着相对较小的作用。
