论文标题
激光诱导的氨的超快伞运动的电子衍射
Laser-induced electron diffraction of the ultrafast umbrella motion in ammonia
论文作者
论文摘要
实时可视化分子转换需要使用Ångström空间和飞秒颞原子分辨率的结构检索方法。含氢分子的成像还需要一种对氢核原子位置敏感的成像方法，大多数方法对氢散射具有相对较低的敏感性。激光诱导的电子衍射（LIED）是一种表面技术，它可以对具有亚Ångström的气相多原子分子的超快结构变化以及对氢散射的敏感性相对较高的敏感性。在这里，我们在其强场电离之后成像一个孤立的氨分子（NH $ _3 $）的雨伞运动。中性氨分子电离后，氨阳离子（NH $ _3^+$）经历了从金字塔（$φ_{hnh} = 107^\ circ $）到平面（$φ_{$φ_{hnh} = 120 = 120^\ $ $）结构的超快几何转化。使用LIED，我们检索了一个接近平面的（$φ_{hnh} = 117 \ pm 5^\ circ $）野外nh $ _3^+$分子结构$ 7.8-9.8 $ fomettoseconds电离后。我们测量的现场穿衣NH $ _3^+$结构与我们使用量子化学量从头算计算的计算平衡野外结构非常吻合。
Visualizing molecular transformations in real-time requires a structural retrieval method with Ångström spatial and femtosecond temporal atomic resolution. Imaging of hydrogen-containing molecules additionally requires an imaging method that is sensitive to the atomic positions of hydrogen nuclei, with most methods possessing relatively low sensitivity to hydrogen scattering. Laser-induced electron diffraction (LIED) is a table top technique that can image ultrafast structural changes of gas-phase polyatomic molecules with sub-Ångström and femtosecond spatiotemporal resolution together with relatively high sensitivity to hydrogen scattering. Here, we image the umbrella motion of an isolated ammonia molecule (NH$_3$) following its strong field ionization. Upon ionization of a neutral ammonia molecule, the ammonia cation (NH$_3^+$) undergoes an ultrafast geometrical transformation from a pyramidal ($Φ_{HNH} = 107 ^\circ$) to planar ($Φ_{HNH}=120^\circ$) structure in approximately 8 femtoseconds. Using LIED, we retrieve a near-planar ($Φ_{HNH}=117 \pm 5^\circ$) field-dressed NH$_3^+$ molecular structure $7.8-9.8$ femtoseconds after ionization. Our measured field-dressed NH$_3^+$ structure is in excellent agreement with our calculated equilibrium field dressed structure using quantum chemical ab initio calculations.
