Institut für Ionenphysik und Angewandte Physik, Leopold Franzens Universität, Technikerstr. 25, A-6020 Innsbruck, Austria.
Phys Chem Chem Phys. 2009 Nov 14;11(42):9791-7. doi: 10.1039/b913175b. Epub 2009 Aug 27.
Electron impact ionization of argon clusters embedded in helium droplets is investigated. Superior mass resolution makes it possible to distinguish between nominally isobaric cluster ions. An abundance maximum for ArHe(12)(+) is unambiguously confirmed; the spectra also prove the formation of Ar(2)He(n)(+) complexes that had been claimed to fragment into pure Ar(2)(+). Distributions of larger argon cluster ions containing up to 60 atoms closely resemble distributions observed upon electron impact or photoionization of bare argon clusters; caging and evaporative cooling provided by the helium matrix do not suffice to quench fragmentation of the nascent argon cluster ions. Intriguing abundance anomalies are observed in distributions of argon cluster ions that contain water, nitrogen or oxygen impurities. The strong abundance of Ar(55)H(2)O(+), Ar(54)O(2)(+) and Ar(54)N(2)(+) contrasts with the virtual absence of slightly larger cluster ions containing the corresponding impurities. The features are probably related to enhanced cluster ion stability upon closure of the second icosahedral shell but the difference in magic numbers (54 versus 55) and the well-known reactivity of charged argon-nitrogen complexes suggest structural differences.
氩原子团簇嵌入氦液滴中的电子碰撞离化作用得到了研究。优异的质量分辨率使得能够区分名义等压的团簇离子。明确证实了 ArHe(12)(+)的丰度最大值；该光谱还证明了 Ar(2)He(n)(+)配合物的形成，这些配合物据称会碎裂成纯 Ar(2)(+)。包含多达 60 个原子的较大氩原子团簇离子的分布与电子冲击或裸氩原子团簇光致电离时观察到的分布非常相似；氦基质提供的笼和蒸发冷却不足以阻止初生氩原子团簇离子的碎裂。在含有水、氮或氧杂质的氩原子团簇离子分布中观察到有趣的丰度异常。Ar(55)H(2)O(+)、Ar(54)O(2)(+)和 Ar(54)N(2)(+)的强烈丰度与含有相应杂质的稍大的团簇离子的虚拟缺失形成鲜明对比。这些特征可能与闭合第二个二十面体壳时增强的团簇离子稳定性有关，但由于魔术数（54 与 55）的差异以及已知的带电氩-氮配合物的反应性，表明存在结构差异。
