Water ice is an important medium in astrochemistry, primarily in the form of mantles that form on dust particles within dense interstellar clouds and beyond the water snow line in protoplanetary nebulae. Chemistry is often quite different on or within water ice compared to the gas phase. One of the biggest reasons for this is that charged species, both cations and anions, are stabilized relative to neutral species in ice because the interactions of charged species with water are far stronger than the interactions of neutral species with water. Theoretical cluster studies readily demonstrate that reactions in which charged species are stabilized is an emergent phenomenon that depends on cluster size. In some cases, these <i>charge shift reactions</i> become operative with just a few waters, such as acid-to-base proton transfer reactions between acids like HNCO, HCOOH, and HCN and ammonia. In other cases, more water molecules are needed to induce charge shift. Clusters with 12 to 20 waters are large enough to observe numerous reaction types and have also been shown to be sufficiently large to produce both vibrational and electronic spectra of predictive value for experimental studies (with certain caveats and limitations). Various families of charge shift reactions will be described, focusing on recent study of the interaction of the CO cation with ice.

Theoretical cluster studies of charge shift reactions in astrophysical ices

253rd National Meeting (2017)

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