43 research outputs found
Induced ionization of small molecules: comparison of experiment with quantum and classical calculations
Multiple ionization of rare gases by hydrogen-atom impact
Cross sections for the multiple ionization of He, Ne, Ar, and Kr by H^0 impact with and without the simultaneous ionization (electron loss) of the projectile are presented in the energy range 75–300 keV. The data were measured by coincident detection of the recoil target ions and the charge-state analyzed scattered projectiles. To obtain information about the role played by the electron of H^0 in the collision, the measurements were repeated with protons under the same experimental conditions. The measured data are analyzed using the classical trajectory Monte Carlo (CTMC) method. CTMC describes well the experimental data for both projectiles for single vacancy creation; however, increasing deviation is observed between theory and experiment with increasing number of created vacancies and with decreasing target atomic number
Anion emission from water molecules colliding with positive ions: Identification of binary and many-body processes
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.Comment: 5 pages, 4 figure
Ionization of small molecules induced byH+, He+, andN+projectiles: Comparison of experiment with quantum and classical calculations
We report the energy and angular distribution of ejected electrons from
CH and HO molecules impacted by 1 MeV H, He and 650 keV N
ions. Spectra were measured at different observation angles, from 2 eV to 2000
eV. The obtained absolute double-differential-electron-emission cross sections
(DDCS) were compared with the results of CTMC and CDW-EIS calculations. For the
bare H+ projectile both theories show remarkable agreement with the experiment
at all observed angles and energies. The CTMC results are in similarly good
agreement with the DDCS spectra obtained for impact by dressed He and N
ions, where screening effects and electron loss from the projectile gain
importance. The CDW-EIS calculations slightly overestimate the electron loss
for 1 MeV He impact, and overestimate both the target and projectile
ionization at low emitted electron energies for 650 keV N impact. The
contribution of multiple electron scattering by the projectile and target
centers (Fermi-shuttle) dominates the N-impact spectra at higher electron
energies, and it is well reproduced by the non-perturbative CTMC calculations.
The contributions of different processes in medium velocity collisions of
dressed ions with molecules are determined
Mid-IR and VUV spectroscopic characterisation of thermally processed and electron irradiated CO2 astrophysical ice analogues
Molecular-rotation-induced splitting of the binary ridge in the velocity map of sub-eV H+ ions ejected from H2 molecules by ion impact
In studies of ion-induced molecular fragmentation, the challenging measurement of the velocity distribution of fragments emitted below 1-eV kinetic energy is rarely achieved, although most fragments have an energy below this value. Here, we study H+ fragment emission in collisions of 10-keV O+ ions with H2 molecules using a field-free time-of-flight technique developed specifically to detect sub-eV fragments. We find that, in the velocity map, the binary ridge due to direct H+ knockout is split into two parts arising from the rotational motion of the H2 molecule, and that this split scales with rotational velocity. The velocity distribution of the nuclei in the original molecule is determined and the thermally populated J = 1 rotational level is found to be the dominant contributor, although asymmetry in the split indicates projectile-induced rotational transitions between M sub-levels. These rotation effects influence fragment emission probabilities, thus carrying important consequences for the radiation-induced hydrogen loss and H2 dissociation in the atmospheres or exospheres of planets and moons