From atoms to aerosols: probing clusters and nanoparticles with synchrotron based mass spectrometry and X-ray spectroscopy
Tunable synchrotron radiation provides a universal yet selective scalpel to decipher molecular information in complex chemical systems when coupled to mass spectrometry and X-ray spectroscopy. At the Chemical Dynamics Beamline, the radiation emanating from the Advanced Light Source at Berkeley has been utilized by physical chemists and chemical physicists to probe chemical reactivity, energetics and spectroscopy for over two decades. Emerging themes are the study of molecular growth mechanisms, solvation, electronic structure and reactivity in clusters, complexes and nanoparticles. The ion-induced and neutral growth mechanisms in methanol and acetylene clusters are revealed by vacuum ultraviolet (VUV) single photon ionization mass spectrometry. The photoionization dynamics of glycerol show signatures of strong ionic hydrogen bonds, non-covalent interactions are explored in naphthalene water clusters, proton transfer pathways are revealed in acetaldehyde water clusters, and exciton charge transfer is probed in argon water clusters. X-ray spectroscopy provides a local probe of a sample's electronic structure with elemental and site-specificity and is thus ideally suited for probing solvation. Velocity map imaging X-ray photoelectron spectroscopy coupled to nanoparticle beams that allows for the visualization of dynamic processes in solvation and molecular growth processes is described. This technique is used to probe reactivity in aerosol chemistry, obtain phase and pH dependent information on aqueous nanoparticles and electron scattering cross-sections from hydrocarbon nanoparticles. We describe future opportunities in probing elusive radicals such as the cyclic 3,5-dehydroxyphenyl radical cation and excited states in water clusters formed in VUV photoionization, explore reactivity in confined spaces via X-ray spectroscopy and elucidate time dynamics with laser-synchrotron pump probe experiments.