Single-electron Capture In Collisions Research Articles

Study of state-selective single-electron capture in slow Ne7+ colliding with He and H2 target

Using the cold target recoil-ion momentum spectroscopy, we measured the state-selective single electron capture in collisions of 3.5–6.3 keV u−1 Ne7+ ions and He and H2. The Q-value spectra and angular distributions as a function of the projectile incident energy were obtained. The results show that the single electron capture into n = 4 states is the dominant reaction channel for the Ne7+-He system, while the capture into n = 4 and n = 5 states both are dominant processes for the Ne7+-H2 system. The molecular coulombic barrier model and the potential energy curves can qualitatively explain the measured state populations for both systems.

Single Electron Capture in Collisions of Fast Ions with Molecular Hydrogen in the Impact Parameter Representation

Single Electron Capture in Collisions of Fast Ions with Molecular Hydrogen in the Impact Parameter Representation

Single-electron capture in collisions of positively charged muons with hydrogen and helium atoms

The prior form of the three-body boundary-corrected first Born (CB1-3B) method is used to calculate the state-selective total cross sections for single-electron capture into 1s, 2s and 2s final states of a fast muon projectiles from a ground-state hydrogen and helium targets at energies 10 keV to 1 MeV. For helium target, the frozencore approximation and the independent particles model were used. The state-summed total cross sections for electron capture into all final states of the muonium systems (?+,e) are obtained by applying the Oppenheimer (n?3) scaling law. Unfortunately, there are no available experimental data, so our theoretical results were compared to the CDW-3B theoretical results.

Kinetic energy distributions of the fragment ions from multiply ionized C2H6 as functions of the charge state of the intermediate states

Here, we report the kinetic energy distributions (KEDs) of the fragment ions produced from multiply ionized ethane (C2H6) molecules in single electron capture collisions with 1.2 MeV C2+. To systematically investigate the fragmentation dynamics, the KEDs were obtained as functions of the charge state of the intermediate C2H6r+* ions r transiently generated prior to fragmentation. r was determined from coincidence measurement of the fragment ions and the number of emitted electrons. The KEDs are drastically different depending on the number of broken C–H bonds. The underlying causes are explained by the variation of the relative contributions of the multiply ionized states and preferential fragmentation pathways. For instance, CHn+ fragment ions with smaller n exhibit lower KEs because they are likely to be correlated with H+ emission, which carries away a large portion of the KE release. In addition, we report the KEDs of H3+ produced from doubly and triply charged states.

Fragmentation of multiply ionized biomolecules induced by MeV heavy ions

SynopsisCollision-induced ionization and fragmentation of gas-phase adenine molecules (C5N5H5) have been investigated for single electron capture collisions of 1.2 MeV C2+ ions. Coincidence measurements between the number of ejected electrons and the time-of-flight of fragment ions allows us to determine charge states of intermediate parent ions r. Highly charged parent ions are observed up to r ∼ 6 and the production of lighter fragment ions becomes predominant with increasing r. We found that kinetic energies of H+ are significantly larger than those of other fragment ions and become nearly equivalent irrespective of r for r > 1.

Single-electron capture collisions of ground and metastable Ne2+ ions with molecular gases

Using the translational energy-gain spectroscopy technique, we have measured the energy-gain spectra and absolute total cross sections for single-electron capture in collisions of Ne2+ with N2, CO2 and H2O at laboratory impact energies between 50 and 400 eV and 0° scattering angles. In all the collision systems studied here, reaction channels have been observed which indicate the presence of the long-lived metastable states of (2s2 2p4 1D and 1S) in the Ne2+ incident beam. These measurements also indicate that capture from the metastable states into excited states of the projectile product ions is the most important inelastic process. Contributions from capture accompanied by the excitation and ionization of the target product are also detected. In addition, the energy dependence of the total single-electron capture cross sections is studied and found to slowly increase with increasing impact energy. The present data are compared with the theoretical calculations of the classical over the barrier, extended classical over the barrier and Landau–Zener models.

Absolute detection efficiencies for keV energy atoms incident on a microchannel plate detector

The absolute detection efficiencies of a microchannel plate detector (MCP) were determined experimentally for neutral hydrogen, carbon, and tungsten atoms with impact energies of 0.5–4.5keV. We measured detection efficiencies using our recently developed method, which uses coincidence counting between neutralized incident ions and ionized target atoms in single-electron capture collisions. The obtained detection efficiencies showed similar impact-energy and mass dependence to those of rare gas atoms (Ne, Ar, Kr, and Xe), measured previously using our method. The detection efficiencies increased with increasing impact energy and converged to the open area ratio (∼50%) of the MCP used. The efficiencies at fixed energies decreased as the mass of the incident atom increased. The absolute detection efficiencies obtained for H, C, W, Ne, Ar, Kr, and Xe atoms could be scaled according to the average electron emission yield estimated using the formulas for electronic and nuclear stopping powers.

Angular- and state-selective differential cross sections for single-electron capture inp-He collisions at intermediate energies

State-selective electron capture cross sections and projectile scattering-angle differential cross sections for single-electron capture in collisions of protons with He at energies ranging from 50 to 100 keV have been experimentally investigated by means of a reaction microscope. It is shown that for single-electron capture the ground-state transfer is the dominant reaction channel, and excited-state transfer has relative small contributions to the cross sections. The transfer-excitation process has a minor contribution to the total cross sections. As the projectile energy increases, ground-state transfer remains dominant, but the relative contributions of the excited-state transfers become more important. The minor contribution of transfer excitation remains almost unchanged. Furthermore, it was found that for single transfer the present results are in good agreement with independent electron model predictions in the energy regime considered. For transfer excitation, however, there are obvious discrepancies between our measurements and theoretical results. We concluded that the electron-electron-correlation effects may play a role at least in transfer excitation in collisions of protons with He in the energy range considered.

State-selective electron capture by O3+ ions on He and H2

Using the cold target recoil ions momentum spectroscopy, we have studied single electron capture in collisions of O3+ ions with He and H2 at 60 keV. The state-selective, angular differential cross sections have been determined by measuring the transverse and longitudinal momentum of recoil ion. The dominant reaction channel is single electron capture into the O2+(2s2p3) and O2+(2s22p3l) states for He and H2 target respectively. The experimental results could be qualitatively understood by reaction windows of the classical over-barrier model.

State-selective electron capture in He++ H2collisions at intermediate impact energies

State-selective single electron capture in collisions of He${}^{+}$ with H${}_{2}$ molecules is investigated using the cold-target recoil-ion momentum spectroscopy technique. The energy range considered is 6.25 keV/amu (projectile velocity ${v}_{p}$ $=$ 0.5 a.u.) to 50 keV/amu (${v}_{p}$ $=$ 1.41 a.u.). In addition, we explore the transverse recoil momentum distributions that provide direct access to the angular scattering of the receding projectile. The present experimental data are contrasted to the theoretical results obtained by means of the classical trajectory Monte Carlo model with which we find good overall agreement in the energy range explored.

Single electron capture in collisions of Nq+ (q = 5, 6, 7) ions with helium

Close-coupling calculations are carried out for cross sections of the single electron capture in collisions of Nq+(q = 5, 6, 7) ions with helium atoms in the collision velocity range from 0.3 a.u. to 1.8 a.u. The relative importances of the single ionization (SI) to the single capture (SC) are investigated for the Nq+(q = 5, 6, 7) projectiles, respectively. The SI/SC cross section ratio for the N7+ projectile obtained from our calculations is in excellent agreement with the experimental data. The ratio curves also show us distinct behaviours when the charge of the projectile is different. The partial electron capture cross sections for different projectiles indicate that the electron on the target He atom tends to be captured by the projectile into its lower orbital of the outer shell with the decreasing projectile charge.

Single-electron-capture processes in collisions of He2+, Liq+ (q=1,2,3),C6+, andO8+ions with helium

Cross sections for single-electron capture in collisions of He${}^{2+}$, Li${}^{q+}$ ($q$ = 1,2,3), ${\mathrm{C}}^{6+}$, and ${\mathrm{O}}^{8+}$ ions with helium atoms at incident energy ranging from 50 to 5000 keV/amu have been calculated in the framework of four-body boundary-corrected continuum intermediate state (BCCIS-4B) approximation in both prior and post forms. In this formalism, distortion in the final channel related to the Coulomb continuum states of the projectile ion and the active electron in the field of residual target ion are included. In all cases, total single-electron-capture cross sections have been calculated by summing over all contributions up to $n$ = 3 shells and subshells, respectively. It has been observed that the contribution of the capture cross section into the excited states is significant for asymmetric collision (${Z}_{P}>{Z}_{T}$) and is insignificant for symmetric collision. Numerical results for the total cross sections show good agreement with the available experimental findings, particularly in the post form. Post-prior discrepancy has been found to be within 30% except for Li${}^{+}$ + He interactions below 150 keV/amu.

State-selective electron capture inHe32++He collisions at intermediate impact energies

In this work we have measured single-electron capture in collisions of $^{3}\mathrm{He}$${}^{2+}$ projectiles incident on a helium target for energies of 13.3--100 keV/amu with the cold-target recoil-ion momentum spectroscopy setup implemented at the Centro At\'omico Bariloche. State-selective single-capture cross sections were measured as a function of the impact energy. They were found to agree with previous existing data from the Frankfurt group, starting at the impact energy of 60 keV/amu; as well as with recent data, at 7.5 keV/amu, from the Lanzhou group. The present experimental results are also contrasted to the classical trajectory Monte Carlo method with dynamical screening.

Single-electron capture in collisions of proton beams with molecules of biological interest

Single-electron charge exchange from simple molecular targets of biological interest to fast ion beams is investigated using the continuum-distorted-wave-eikonal-initial-state model. Thus, this model is applied for electron capture from molecules with many orbitals in the fundamental state. The role played by the representation of the initial state is analyzed and contributions from different molecular orbitals to total cross sections are calculated. The results are shown to be in very good agreement with existing experimental data for collision energies larger than a few tens of keV.

Single-electron capture cross-sections for W+ and W2+ ions colliding with inert gas and hydro-carbon molecular gas targets

Absolute cross-sections for single-electron capture collisions of singly and doubly charged tungsten ions with inert gas (He, Ne, Ar, and Kr) and hydro-carbon gas (H2, CH4, C2H6, and C3H8) targets were derived experimentally. The measured cross-sections show strong power-law dependence on the first ionization potential of the target, whose slopes are independently identical to inert and hydro-carbon gas targets.

Cross sections for single electron capture in collisions of N2+ with He at low energies

The absolute cross sections of single electron capture during the collision of N2+ with He have been measured over the energy range 0.1-300 eV/u. From the plot showing the dependence of cross sections on energy, the following three remarkable observations can be made: (1) the cross sections exhibit an oscillatory structure below 1eV/u, (2) a bend in the cross sections appears at approximately 1 eV/u and (3) there is a dip in the cross sections at approximately 70 eV/u. The formation of an oscillatory structure is attributed to the glory effect. The bend in the cross sections occurs owing to the attractive potential part of a l2n state of quasimolecule NHe2+. The dip in the cross sections appears as a result of opening a new reaction path above 70eV/u. The glory effect can be observed for the first time on a total cross section even for slow ion-neutral collisions. The objective of this study is to explore the possibilities of providing a detailed explanation of energy dependence measurements in order to study reaction dynamics for a charge changing process.

Recoil momentum of molecular ions in collisions of Ar6++N2 at energies below 300 eV/u

To elucidate the collision energy dependence of the recoil momentum of molecular ions after electron transfer, we measure the recoil momentum of non-dissociated molecular ions for single electron capture collisions of Ar6+ with N2 at collision energies from 7.5 to 240 eV/u. The measured collision energy dependence of the recoil momentum is compared with those obtained by a theoretical calculation using a deflection function with polarization potential. We obtain fairly good agreement between the measured and calculated results.

State selective capture by highly charged Xe ions

Single-electron capture in collisions of highly charged ions Xe18+ and Xe24+ with Na atoms is investigated by measuring the momenta of the Na recoil ions. The Q-value spectrum in Xe18+ + Na collisions shows capture into lower n states compared with Classical over-barrier model (CBM) calculations. Partial cross sections for capture into n = 13…20 for Xe18+and n = 19… 24 for Xe24+, extracted from Q-value spectra, show no obvious dependence in the energy range available for our experiment (0.5-4.5 keV/amu).

Electron capture by O3+ ions from He, H2O and CO2

Using the translational energy-gain spectroscopy technique, we have measured the energy-gain spectra and absolute total cross sections for single-electron capture in collisions of O3+ ions with He, H2O and CO2 at impact energies between 0.3 and 1.2 keV and scattering angles between 0° and 6°. At the lowest collision energy, 300 eV, the energy-gain spectrum for O3+ - He collisions indicates that single-electron capture into the 2s2p3 3P state of the product O2+ is the dominant reaction channel observed with smaller contributions from capture into the 2s2p3 1D, 3S and 1P states. For O3+ - H2O collisions, the dominant peak correlates with capture into the 2p3p state of O2+, with a significant contribution involving capture into the 2p3s state. In O3+ - CO2 collisions, the dominant reaction channel is due to capture into the 2p3s state of O2+, with contributions from capture into the 2p3p state. The measured cross sections are compared with the available measurements and theoretical results based on the multi-channel Landau-Zener (MCLZ) model.

Energy gain spectroscopy of multiply charged light ions in collisions with hydrogen at 50 eV/u

We have measured energy gain spectra for single-electron capture collisions of Helike C, N and O ions with H2 at 50 eV/u. Energy gain spectra were examined with energy gain functions calculated from a classical over barrier model, and we obtained fairly good agreement between experimental and calculated results. We find that single electron capture occurs predominantly for C4+ and O6+ ions, while for N5+ ions double electron capture followed by transfer ionization is the dominant process in the formation of N3+ions.