Infrared Multiple Photon Dissociation of Cesium Iodide Clusters Doped with Mono-, Di- and Triglycine

Charged cesium iodide clusters doped with mono-, di- and triglycine serve as a model system for sea salt aerosols containing biological molecules. Here, we investigate reactions of these complexes under infrared irradiation, with spectra obtained by infrared multiple photon dissociation (IRMPD). The cluster ions are generated via electrospray ionization and analyzed in the cell of a Fourier Transform Ion Cyclotron Resonance (FT-ICR) Mass Spectrometer. Depending on the cluster size and peptide length, loss of HI or loss of a glycine unit is observed. The experimental measurements are supported by quantum chemical calculations. We show that N-H and O-H stretching modes dominate the spectrum, with large shifts depending on local interactions, namely due to interaction with iodide anions or intramolecular hydrogen bonding. Both experiment and theory indicate that several isomers are present in the experimental mixture, with different IR fingerprints as well as dissociation pathways.