Hydration motifs of ammonium bisulfate clusters show complex temperature dependence

The role of water in the formation particles from atmospheric trace gases is not well understood, large part due to difficulties detecting its presence under conditions and variety possible structures that must be screened computationally. Here, we use infrared spectroscopy variable-temperature ion trap mass spectrometry investigate structural motifs adopted by bound ammonium bisulfate clusters their temperature dependence. For featuring only acid–base linkages, adopts a bridging arrangement spanning an adjacent bisulfate. larger clusters, can also insert into bisulfate–bisulfate hydrogen bond, yielding hydration isomers with very similar binding energies. population these shows complex evolution, as apparent third isomer appears dependence difficult explain using simple thermodynamic arguments. These observations suggest thermodynamics such may straightforward.