A size resolved investigation of large water clusters

Abstract

Size selected water clusters are generated by photoionizing sodium doped clusters close to the ionization threshold. This procedure is free of fragmentation. Upon infrared excitation, size- and isomer-specific OH-stretch spectra are obtained over a large range of cluster sizes. In one application of this method the infrared spectra of single water cluster sizes are investigated. A comparison with calculations, based on structures optimized by genetic algorithms, has been made to tentatively derive cluster structures which reproduce the experimental spectra. We identified a single all-surface structure for n = 25 and mixtures with one or two interior molecules for n = 24 and 32. In another application the sizes are determined at which the crystallization sets in. Surprisingly, this process strongly depends on the cluster temperature. The crystallization starts at sizes below n = 200 at higher temperatures and the onset is shifted to sizes above n = 400 at lower temperatures.

Extensive water cluster fragmentation after low energy electron ionization

“…Although, we have recently 105 demonstrated that this method is not universal and possible reactions of sodium with cluster constituents can lead to unexpected results [41], for the pure water clusters this method yields the neutral cluster size distributions [32]. More details can be found in [32,40,45,43,44,33,35].…”

“…Later on it was suggested by Signorells' group as a "sizer for weakly bound ultrafine A c c e p t e d M a n u s c r i p t aerosol particles" due to the fragmentation-free ionization [33]. It is also used in Zeuchs' group in connection with the vibrational spectroscopy of large size 95 selected clusters [42,43,44]. Yet, the implementation of this method as the sizer for neutral clusters is still relatively new and scarce.…”

Infrared spectroscopy of O˙− and OH− in water clusters: evidence for fast interconversion between O˙− and OH˙OH−

“…From previous studies of neutral water clusters, [45][46][47] we can assign the broad absorption feature (3000-3600 cm À1 ) with a maximum around 3450 cm À1 to the O-H stretching vibrations of water molecules that are hydrogen bonded in the cluster. A sharp and, at least for the larger clusters, well-separated free O-H stretch near 3700 cm À1 is attributed to water molecules on the cluster surface.…”

Probing RbBr solvation in freestanding sub-2 nm water clusters

“…This even though water clusters quite likely present a different type of environment for the salt ions in terms of e.g. temperature and structure 11 . We cannot however rule out the possibility that such differences arise as models and assumptions used to describe for example the pick-up process, solvation and different spectral features are refined.…”

“…In general, ion pairing increases as a function of solution concentration and temperature and decreases as a function of solvent relative permittivity (dielectric constant). Studying this phenomenon in nanoscale water clusters provides an interesting comparison as for example the cluster temperature can be severely reduced compared to bulk aqueous system without turning into solid 11 . Also, the high number of surface molecules in relation to the bulk molecules and the reduced size of the system could alter the solvation dynamics, especially when segregation effects of ions are present.…”