The spectroscopy of free radicals and radical containing entrance-channel complexes embedded in superfluid helium nano-droplets is reviewed. The collection of dopants inside individual droplets in the beam represents a micro-canonical ensemble, and as such each droplet may be considered an isolated cryo-reactor. The unique properties of the droplets, namely their low temperature (0.4 K) and fast cooling rates ($\sim10^{16}$ K s$^{-1}$) provides novel opportunities for the formation and high-resolution studies of molecular complexes containing one or more free radicals. The production methods of radicals are discussed in light of their applicability for embedding the radicals in helium droplets. The spectroscopic studies performed to date on molecular radicals and on entrance / exit-channel complexes of radicals with stable molecules are detailed. The observed complexes provide new information on the potential energy surfaces of several fundamental chemical reactions and on the intermolecular interactions present in open-shell systems. Prospects of further experiments of radicals embedded in helium droplets are discussed, especially the possibilities to prepare and study high-energy structures and their controlled manipulation, as well as the possibility of fundamental physics experiments.
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机译:综述了嵌入超流氦纳米液滴中的自由基和包含自由基的入口通道络合物的光谱。束中单个液滴内部的掺杂物的收集代表了微规范的集合,因此每个液滴都可以被认为是一个隔离的低温反应器。液滴的独特特性,即它们的低温(0.4 K)和快速冷却速率($ \ sim10 ^ {16} $ K s $ ^ {-1} $),为液滴的形成和高分辨率研究提供了新的机会。含有一个或多个自由基的分子复合物。根据自由基在氦气小滴中嵌入的适用性,讨论了自由基的产生方法。迄今为止,已对分子自由基以及自由基与稳定分子的进入/退出通道络合物进行了光谱研究。观察到的配合物提供了一些基本化学反应的势能面以及开壳系统中存在的分子间相互作用的新信息。讨论了嵌入氦滴中的自由基进一步实验的前景,尤其是制备和研究高能结构及其受控操纵的可能性以及基础物理实验的可能性。
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