The adsorption of up to ∼100 helium atoms on cations of the planar polycyclic aromatic hydrocarbons (PAHs) anthracene, phenanthrene, fluoranthene, and pyrene was studied by combining helium nanodroplet mass spectrometry with classical and quantum computational methods. Recorded time-of-flight mass spectra reveal a unique set of structural features in the ion abundance as a function of the number of attached helium atoms for each of the investigated PAHs. Path-integral molecular dynamics simulations were used with a polarizable potential to determine the underlying adsorption patterns of helium around the studied PAH cations and in good general agreement with the experimental data. The calculated structures of the helium–PAH complexes indicate that the arrangement of adsorbed helium atoms is highly sensitive toward the structure of the solvated PAH cation. Closures of the first solvation shell around the studied PAH cations are suggested to lie between 29 and 37 adsorbed helium atoms depending on the specific PAH cation. Helium atoms are found to preferentially adsorb on these PAHs following the commensurate pattern common for graphitic surfaces, in contrast to larger carbonaceous molecules like corannulene, coronene, and fullerenes that exhibit a 1 × 1 commensurate phase.

中文翻译：

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小阳离子多环芳烃吸附氦：烃结构对微溶剂化模式的影响

通过将氦纳米液滴质谱与经典和量子计算方法相结合，研究了多达 100 个氦原子在平面多环芳烃 (PAH) 蒽、菲、荧蒽和芘的阳离子上的吸附。记录的飞行时间质谱揭示了一组独特的离子丰度结构特征，作为每个研究的多环芳烃的附加氦原子数的函数。使用具有极化势的路径积分分子动力学模拟来确定所研究的 PAH 阳离子周围氦的潜在吸附模式，并且与实验数据基本一致。氦-PAH 复合物的计算结构表明吸附的氦原子排列对溶剂化 PAH 阳离子的结构高度敏感。根据特定的 PAH 阳离子，建议在所研究的 PAH 阳离子周围的第一个溶剂化壳的闭合位于 29 到 37 个吸附的氦原子之间。发现氦原子优先吸附在这些多环芳烃上石墨表面常见的相称模式，与表现出 1 × 1 相称相的较大碳质分子（如环烯、晕烯和富勒烯）形成对比。