Structural isomer population of a hydrogen-bonded cluster generally depends on temperature. Therefore, determination of an isomer population profile in a wide temperature range is important to understand the nature of hydrogen bond networks of the cluster. To explore an isomer population profile, stepwise changes of internal vibrational energy of a protonated hydrogen-bonded cluster are performed by inert gas tagging. We observe infrared spectra of the protonated methanol pentamer with various tag species. The bare protonated methanol pentamer practically has only two possible isomer types. With the tagging, the relative population of the two isomer types changes according to the binding energy with the tag species. The observed relative population follows its theoretically predicted temperature dependence.

中文翻译：

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惰性气体标记法对质子化甲醇簇的内部能量的逐步变化

氢键团簇的结构异构体总体上取决于温度。因此，在较宽的温度范围内确定异构体的总体分布对于理解该簇的氢键网络的性质很重要。为了探索异构体的分布图，质子化氢键团簇的内部振动能的逐步变化是通过惰性气体标记进行的。我们观察到具有各种标签种类的质子化甲醇五聚体的红外光谱。裸质子化甲醇五聚体实际上仅具有两种可能的异构体类型。通过标记，两种异构体类型的相对种群根据与标记物质的结合能而变化。观察到的相对种群遵循其理论上预测的温度依赖性。