Tautomers are ubiquitous throughout chemistry and typically considered inseparable in solution. Yet (bio)chemical activity is highly tautomer-specific, with common examples being the amino and nucleic acids. While tautomers exist in an equilibrium in solution, in the cold environment of a molecular beam the barrier to tautomerization is typically much too high for interconversion, and tautomers can be considered separate species. Here we demonstrate the first separation of tautomers within a molecular beam and the production of tautomerically pure gas-phase samples. We show this for the 2-pyridone/2-hydroxypyridine system, an important structural motif in both uracil and cytosine. Spatial separation of the tautomers is achieved via electrostatic deflection in strong inhomogeneous fields. We furthermore collect tautomer-resolved photoelectron spectra using femtosecond multiphoton ionization. This paves the way for studying the structure–function–dynamic relationship on the level of individual tautomers, using approaches that typically lack the resolution to do so, such as ultrafast dynamics experiments.

中文翻译：

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静电偏转法制备互变异构体纯分子束

互变异构体在整个化学过程中无处不在，通常被认为在溶液中不可分离。然而，（生物）化学活性具有高度的互变异构体特异性，常见的例子是氨基酸和核酸。虽然互变异构体在溶液中以平衡状态存在，但在分子束的冷环境中，互变异构化的障碍通常对于相互转化来说太高，并且互变异构体可以被认为是单独的物种。在这里，我们展示了分子束内互变异构体的首次分离以及互变异构纯气相样品的生产。我们针对 2-吡啶酮/2-羟基吡啶系统展示了这一点，该系统是尿嘧啶和胞嘧啶的重要结构基序。互变异构体的空间分离是通过强不均匀场中的静电偏转实现的。我们还使用飞秒多光子电离收集互变异构体分辨的光电子能谱。这为使用通常缺乏分辨率的方法（例如超快动力学实验）研究单个互变异构体水平上的结构-功能-动力学关系铺平了道路。