Electron Capture In Collisions Research Articles

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.

Determination of the solid angle and response function of a hemispherical spectrograph with injection lens for Auger electrons emitted from long lived projectile states.

We present SIMION 8.1 Monte Carlo type simulations of the response function and detection solid angle for long lived Auger states (lifetime τ ∼ 10(-9) - 10(-5) s) recorded by a hemispherical spectrograph with injection lens and position sensitive detector used for high resolution Auger spectroscopy of ion beams. Also included in these simulations for the first time are kinematic effects particular to Auger emission from fast moving projectile ions such as line broadening and solid angle limitations allowing for a more accurate and realistic line shape modeling. Our results are found to be in excellent agreement with measured electron line shapes of both long lived 1s2s2p(4)P and prompt Auger projectile states formed by electron capture in collisions of 25.3 MeV F(7+) with H2 and 12.0 MeV C(4+) with Ne recorded at 0° to the beam direction. These results are important for the accurate evaluation of the 1s2s2p (4)P/(2)P ratio of K-Auger cross sections whose observed non-statistical production by electron capture into He-like ions, recently a field of interesting interpretations, awaits further resolution.

Atomic Physics with Accelerators: Projectile Electron Spectroscopy (APAPES)

The new research initiative APAPES (http://apapes.physics.uoc.gr/) has already established a new experimental station with a beam line dedicated for atomic collisions physics research, at the 5 MV TANDEM accelerator of the National Research Centre "Demokritos" in Athens, Greece. A complete zero-degree Auger projectile spectroscopy (ZAPS) apparatus has been put together to perform high resolution studies of electrons emitted in ion-atom collisions. A single stage hemispherical spectrometer with a 2-dimensional Position Sensitive Detector (PSD) combined with a doubly-differentially pumped gas target will be used to perform a systematic isoelectronic investigation of K-Auger spectra emitted from collisions of preexcited and ground state He-like ions with gas targets using novel techniques. Our intention is to provide a more thorough understanding of cascade feeding of the 1s2s2p 4P metastable states produced by electron capture in collisions of He-like ions with gas targets and further elucidate their role in the non-statistical production of excited three-electron 1s2s2p states by electron capture, recently a field of conflicting interpretations awaiting further resolution. At the moment, the apparatus is being completed and the spectrometer will soon be fully operational. Here we present the project progress and the recent high resolution spectrum obtained in collisions of 12 MeV C4+ on a Neon gas target.

Radiative lifetime of the1S0metastable state in doubly charged Kr ions

The radiative lifetime of the $4{s}^{2}4{p}^{4}{\phantom{\rule{0.16em}{0ex}}}^{1}{S}_{0}$ metastable state in $\mathrm{K}{\mathrm{r}}^{2+}$ ions has been experimentally determined using an electrostatic ion trap of the ion-beam storage type. The radiative lifetime was obtained by measuring the number of 350-nm photons emitted during the ${}^{1}{S}_{0}{\ensuremath{\rightarrow}}^{3}{P}_{1}$ magnetic dipole transition of $\mathrm{K}{\mathrm{r}}^{2+}$ as a function of the storage time. The storage lifetime of the $\mathrm{K}{\mathrm{r}}^{2+}$ beam in the trap, which is a correction term in the determination of the radiative lifetime, was measured by detecting Kr neutrals produced by electron capture collisions with residual gases in the trap. We have obtained a lifetime value of $17.4\ifmmode\pm\else\textpm\fi{}0.4\phantom{\rule{0.16em}{0ex}}\mathrm{ms}$, which is larger than the previous experimental results, but consistent with theoretical predictions.

Calculation of total cross sections for electron capture in collisions of Carbon ions with H(D,T)(1s)

The calculations of total cross sections of electron capture in collisions of Cq+ with H(1s) are reviewed. At low collision energies, new calculations have been performed, using molecular expansions, to analyze isotope effects. The Classical Trajectory Monte Carlo method have been also applied to discuss the accuracy of previous calculations and to extend the energy range of the available cross sections.

Comparative study of single and double electron capture from atoms by fast bare ions

Total cross sections for single and double electron capture in collisions of bare ion with helium-like atoms are calculated at energies ranging from 50 to 6,000 keV/amu. The present calculations are carried out using four-body formalism of Coulomb–Born distorted wave formalism and boundary corrected continuum intermediate state approximation. We have made a comparison between single and double electron capture cross sections using both the methods in wide range of energies at different charge state of the projectile. Total cross sections have been calculated by summing over all the contributions up to n = 2 shells and sub-shells. It is also noted that double electron capture cross sections are small thorough out the energy region compared with the single electron capture cross sections. However, the present computed results for asymmetric collisions have been compared with available theoretical and experimental results. We find that our numerical results for total cross sections show good agreement with the available experimental findings.

Electron capture in collisions ofSi3+ions with atomic hydrogen from low to intermediate energies

The electron capture process for the ${\mathrm{Si}}^{3+}$(3$s)$ + H(1$s)$ collisions is investigated by the quantum-mechanical molecular orbital close-coupling (MOCC) method and by the two-center atomic orbital close-coupling (AOCC) method in the energy range of 10${}^{\ensuremath{-}5}$--10 keV/u and 0.8--200 keV/u, respectively. Total and state-selective cross sections are presented and compared with the available theoretical and experimental results. The present MOCC and AOCC results agree well with the experimental measurements, but show some discrepancy with the calculations of Wang et al. [Phys. Rev. A 74, 052709 (2006)] at $E$ > 40 eV/u because of the inclusion of rotational couplings, which play important roles in the electron capture process. At lower energies, the present results are about three to five times smaller than those of Wang et al. due to the difference in the molecular data at large internuclear distances. The energy behaviors of the electron capture cross sections are discussed on the basis of identified reaction mechanisms.

Charge-transfer induced dissociation in the H+(H2O)3-Ar collisions observed with the COINTOF mass spectrometer

Electron-capture in collisions of singly charged protonated water cluster H+(H2O)3, ions with Ar atoms is studied at the impact energy of 8 keV in the frame of the COrrelated Ion and Neutral fragments Time-Of-Flight, COINTOF, technique. In contrast to methods based only on the detection of the charged fragments, dissociation induced by collisional-excitation and electron-capture induced dissociation can be simultaneously recorded in the present set-up. The time of flight measurements of both the neutral and the corresponding charged species resulting from the charge-exchange process provide a direct observation of the dissociation of the neutralized protonated water cluster. Thus, the present COINTOF method provides new valuable insights into the collision process through the detection of produced neutral fragments. Moreover, it opens new possibilities to measure kinetic energy release also in the dissociation of the produced neutrals, which is our future endeavour in the development of the presented COINTOF set up.

State-selective electron capture in collisions of C6+, N7+ with Hydrogen at intermediate energies

We present a joint study of the electron capture process in multicharged ions on atomic Hydrogen at intermediate energies. We have applied two methods, the Eikonal Impulse Approximation (EIA) and the hydrogenic-Classical Trajectory Monte Carlo (CTMC) method. Good agreement is found in both total and state-selective electron capture cross sections.

Fragmentation of molecules under charge-changing collisions of a few MeV heavy ions

We investigated molecular fragmentation of CO and C2H2 molecules by impact of various fast heavy ions. Fragment ions produced in electron capture and loss collisions of projectile ions were measured in coincidence with final projectile charge states. Data acquisition using position sensitive detection system allows us to obtain 3D momentum imaging of fragment ions and kinetic energy release (KER) in various charge-changing collisions. It was found that the KER spectra show strong dependence on the type of charge-changing collisions. This may be caused by the difference of impact parameters associated with individual charge-changing collisions. Moreover we revealed the different fragmentation pathway between ion impacts and photoionization.

Charge-transfer-induced x-ray spectra in collisions ofNe10+with He and Ne atoms

The x-ray spectra resulting from single-electron capture in charge-exchange collisions of Ne${}^{10+}$ with He and Ne atoms are investigated for the projectile energy of 4.54 keV/u using the two-center atomic-orbital close-coupling method. The calculated spectra of the Ne${}^{9+}$ ion produced in Ne${}^{10+}$ + He and Ne${}^{10+}$ + Ne electron-capture collisions have, generally speaking, the same level of agreement with experimental measurements as those calculated previously by the classical trajectory Monte Carlo method, indicating that multi-electron-capture processes, particularly in the case of the Ne${}^{10+}$ + Ne system, significantly affect the considered spectra. The effects of two-electron capture on the spectral line intensity have been demonstrated qualitatively by using the binomial statistics and independent particle model for the target outer-shell electrons. The role of multi-electron-capture processes in the Ne${}^{10+}$ + Ne collision system needs further attention.

Collisions of highly charged ions with hydrogen relevant to plasma diagnostics

We present total cross sections for ionization, and total and nl-partial cross sections for electron capture in collisions of Kr36+ and W60+ with H(1s). Calculations have been carried out using the classical trajectory Monte Carlo method. We have found that scaling laws as functions of the ion charge are valid for total electron capture cross sections, but they are less accurate for n-partial cross sections. The nl-partial cross sections show l distributions similar to those found for collisions with Ar18+ by Errea et al (2006 J. Phys. B: At. Mol. Opt. Phys. 39 L91).

Electron Capture Dissociation and Collision Induced Dissociation of S-Dipalmitoylated Peptides

Here we investigate the effect of S-dipalmitoylation on the electron capture dissociation (ECD) behavior of peptides. The ECD and collision induced dissociation (CID) of peptides modified by covalent attachment of [(RS)-2,3-di(palmitoyloxy)-propyl] (PAM2) group to cysteine residues [C(PAM2)LEYDTGFK and RPPGC(PAM2)SPFK] were examined. The results suggest that ECD of S-dipalmitoylated peptides can provide both primary sequence information and structural information regarding the modification. The structural information provided by CID is complementary to that provided by ECD.

Kinematically complete measurements for electron capture in collision of keV energy ions with atomic and molecular targets

We have performed a kinematically complete experiment to obtain sub-shell resolved differential cross sections for electron capture from inert gas targets in collisions with keV energy singly and doubly charged ions. Measurements were done for single and double capture and transfer ionization using a "reaction microscope".

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.

Electron capture cross section in collision of multi-charged neon ions with ground state hydrogen and helium

The classical trajectory Monte Carlo method and the post form of three-body boundary corrected continuum intermediate state (BCCIS-3B) approximation are employed to calculate the cross sections for total and state-selective electron capture in collision of highly charged Neq+ ions with ground state hydrogen atom in the intermediate to high energy region. In both these methods, the active electron interactions with the partially stripped neon ions are described by a model potential containing both a long-range part and a short-range part. We have also calculated the double electron-capture cross sections in collision of fully stripped neon ion with helium atom in the energy range 80–2,000 keV/amu using the post-form of four-body BCCIS approximation (BCCIS-4B). In BCCIS formalism, the intermediate continuum state of the active electrons with the projectile ion has been taken into account as the projectile charge is greater than the target charge. In addition, state-selective charge transfer cross sections are given in tabular and graphical form.

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.

Multiple ionization and fragmentation of polyatomic molecules by fast heavy ions

We investigated molecular fragmentation for CO, C2H2 and C60 molecules induced by impact of various fast heavy ions. Fragment ions produced in electron capture and loss collisions of projectile ions were measured in coincidence with final projectile charge states. As for C60 target, the number distribution of secondary electrons emitted in single collision event were also measured by means of a triple coincident method. The charge state distribution of transiently formed Cr+60 was successfully reproduced by our new model calculation on the basis of statistical energy deposition model developed for polyatomic molecules. Data acquisition using position sensitive detection system allows us to obtain 3D momentum imaging of fragment ions from CO and C2H2 molecules. Typical results relevant to molecular orientation effect and kinetic energy release (KER) are discussed.

Kinetic-energy release inN2fragmentation by charge-changing collisions of2-MeVC+ions

Collision-induced fragmentation of ${\mathrm{N}}_{2}$ was investigated for 2-MeV ${\mathrm{C}}^{+}$ ions under charge-changing conditions of ${\text{C}}^{+}\ensuremath{\rightarrow}{\text{C}}^{q+}$ ($q=0,2,3$). Coincidence measurement of fragment ions was performed by means of a momentum three-dimensional imaging technique at scattering angles of $\ensuremath{\theta}=0$ and $1.0$ mrad. Kinetic-energy release (KER) obtained for a fragmentation channel of ${\text{N}}_{2}^{2+}\ensuremath{\rightarrow}{\text{N}}^{+}+{\text{N}}^{+}$ was found to differ significantly in electron loss and capture collisions. In two-electron-loss collisions (${\text{C}}^{+}\ensuremath{\rightarrow}{\text{C}}^{3+}$), KER spectra were essentially identical for $\ensuremath{\theta}=0$ and $1.0$ mrad. It is concluded that the energy level of dissociating excited states of ${\mathrm{N}}_{2}^{2+}$ may be saturated when the interaction strength, defined as $\frac{q}{\mathit{vb}}$, exceeds $0.65$, where $q$ and $v$ are the charge and the velocity, respectively, of an incident ion, and $b$ is the impact parameter.