Anion emission from water molecules colliding with positive ions: Identification of binary and many-body processes

TL;DR

This study demonstrates that water molecules emit negative ions when impacted by positive ions at keV energies, revealing the roles of binary and many-body processes in ion-induced anion emission relevant to planetary atmospheres and radiobiology.

Contribution

It provides experimental evidence and modeling of negative ion emission from water due to positive ion collisions, distinguishing binary and many-body process contributions.

Findings

Negative ions are emitted from water upon positive ion impact.

Most emitted ions have low kinetic energy due to many-body processes.

Both nuclear and electronic interactions contribute to ion emission yields.

Abstract

It is shown that negative ions are ejected from gas-phase water molecules when bombarded with positive ions at keV energies typical of solar-wind velocities. This finding is relevant for studies of planetary and cometary atmospheres, as well as for radiolysis and radiobiology. Emission of both H- and heavier (O- and OH-) anions, with a larger yield for H-, was observed in 6.6-keV 16O+ + H2O collisions. The ex-perimental setup allowed separate identification of anions formed in collisions with many-body dynamics from those created in hard, binary collisions. Most of the ani-ons are emitted with low kinetic energy due to many-body processes. Model calcu-lations show that both nucleus-nucleus interactions and electronic excitations con-tribute to the observed large anion emission yield.