Anion emission from water molecules colliding with positive ions: Identification of binary and many-body processes
Résumé
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 experimental setup allowed separate identification of anions formed in collisions with many-body dynamics from those created in hard, binary collisions. Most of the anions are emitted with low kinetic energy due to many-body processes. Model calculations show that both nucleus-nucleus interactions and electronic excitations contribute to the observed large anion emission yield.
Mots clés
Negative ion
H- ion
hydride anion
hydrogen
anion emission
anion formation
water molecule
H2O molecule
gas-phase
collision
atomic collisions
molecular fragmentation
molecular dissociation
charge transfer
electron capture
cross sections
keV energies
two-body processes
binary processes
many-body processes
electronic dissociative excitation
ionization
kinetic energy release
KER
model calculations
MOLPRO
experiment
electrostatic spectroscopy
time of flight
TOF
mass spectroscopy
radiochemistry applications
radiobiology applications
astrophysical applications