The development of ultrafast gas electron diffraction with nonrelativistic electrons has enabled the determination of molecular structures with atomic spatial resolution. It has, however, been challenging to break the picosecond temporal resolution barrier and achieve the goal that has long been envisioned-making space- and-time resolved molecular movies of chemical reaction in the gas-phase. Recently, an ultrafast electron diffraction (UED) apparatus using mega-electron-volt (MeV) electrons was developed at the SLAC National Accelerator Laboratory for imaging ultrafast structural dynamics of molecules in the gas phase. The SLAC gas-phase MeV UED has achieved 65 fs root mean square temporal resolution, 0.63 Å spatial resolution, and 0.22 Å-1 reciprocal-space resolution. Such high spatial-temporal resolution has enabled the capturing of real-time molecular movies of fundamental photochemical mechanisms, such as chemical bond breaking, ring opening, and a nuclear wave packet crossing a conical intersection. In this paper, the design that enables the high spatial-temporal resolution of the SLAC gas phase MeV UED is presented. The compact design of the differential pump section of the SLAC gas phase MeV UED realized five orders-of-magnitude vacuum isolation between the electron source and gas sample chamber. The spatial resolution, temporal resolution, and long-term stability of the apparatus are systematically characterized.

中文翻译：

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飞秒气相兆电子伏特超快电子衍射。

非相对论电子超快气体电子衍射的发展使得能够以原子空间分辨率确定分子结构。然而，打破皮秒时间分辨率障碍并实现长期以来设想的目标——制作气相化学反应的时空分辨分子电影一直是一项挑战。最近，SLAC国家加速器实验室开发了一种使用兆电子伏（MeV）电子的超快电子衍射（UED）装置，用于对气相分子的超快结构动力学进行成像。SLAC气相MeV UED已实现65 fs均方根时间分辨率、0.63 Å空间分辨率和0.22 Å-1倒易空间分辨率。如此高的时空分辨率使得能够捕获基本光化学机制的实时分子电影，例如化学键断裂、开环和穿过圆锥形交叉点的核波包。在本文中，提出了实现 SLAC 气相 MeV UED 的高时空分辨率的设计。SLAC气相MeV UED差动泵部分的紧凑设计实现了电子源和气体样品室之间五个数量级的真空隔离。系统地表征了设备的空间分辨率、时间分辨率和长期稳定性。