Gas-phase cluster ions, consisting of an ion solvated by a number of molecules, can be prepared with a wider range of internal energies (or effective temperatures) than their neutral counterparts. This is primarily due to the strong binding energies that result from ion-molecule interactions. As a result, the structure of these species can vary depending on the temperature. At lower temperatures, enthalpic-favored structures can dominate, while at higher temperatures, entropic-favored structures are preferred. The method of cluster ion formation and/or storage prior to spectroscopic study can have a significant influence on the temperature, which requires some mechanism for either controlling, measuring or modeling the temperature. Using some recent examples from our laboratory, I will discuss how the evaporative ensemble can be used with some degree of confidence in estimating the temperatures of clusters formed by evaporative cooling, by comparing these temperature estimates with direct measurements of rotational state populations and comparison with DFT-MD simulations.<br/>

Assessing internal energy in gas-phase cluster ions: Measurement, modeling and structural effects

251st National Meeting (2016)

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