Positive Atomic Ions Research Articles

Evidence of 1000 eV positive oxygen ion flux generated in reactive HiPIMS plasma

The arrival of highly energetic (near 1000 eV) positive atomic oxygen ions at the substrate region has been detected in a unipolar reactive high-power impulse magnetron sputtering process operated with an uncooled copper target in argon–oxygen mixtures. Examination of the ion fluxes from discharge plasma was performed with a magnetic sector mass-spectrometer and an electrostatic energy analyzer. The energy of fast positive O+ ions is close to the value of eV d (e—elementary charge, V d—discharge voltage), which indicates their connection to the well-studied fraction of negative O− ions, which undergo acceleration in the cathode sheath. After switching the oxygen gas supply off, the flux of energetic O+ species decreases gradually as the poisoned target surface layers become depleted of oxygen due to sputtering in pure argon. Presumably, the observed energetic O+ ions originate as a result of low-angle scattering of fast negative O− ions from other charged or neutral species in the plasma followed by electron detachment, ionization, or charge exchange.

A novel rocket-borne ion mass spectrometer with large mass range: instrument description and first-flight results

Abstract. We present a novel rocket-borne ion mass spectrometer named ROMARA (ROcket-borne MAss spectrometer for Research in the Atmosphere) for measuring atmospheric positive and negative ions (atomic, molecular and cluster ions) and positively and negatively charged meteor smoke particles. Our ROMARA instrument has, compared to previous rocket-borne ion mass spectrometers, a markedly larger mass range of up to m/z 2000 and a larger sensitivity, particularly for meteor smoke particle detection. The major objectives of this first ROMARA flight included the following: a functional test of the ROMARA instrument, measurements between 55 and 121 km in the mass range of atmospheric positive and negative ions, a first attempt to conduct mass spectrometric measurements in the mass range of meteor smoke particles with mass-to-charge ratios up to m/z 2000, and measurements inside a polar mesospheric winter echo layer as detected by ground-based radar. Our ROMARA measurements took place on the Arctic island of Andøya, Norway, at around noon in April 2018 and represented an integral part of the polar mesospheric winter radar echo (PMWE) rocket campaign. During the rocket flight, ROMARA was operated in a measurement mode, offering maximum sensitivity and the ability to qualitatively detect total ion signatures even beyond its mass-resolving mass range. On this first ROMARA flight we were able to meet all of our objectives. We detected atmospheric species including positive atomic, molecular and cluster ions along with negative molecular ions up to about m/z 100. Above m/z 2000, ROMARA measured strong negative-ion signatures, which are likely due to negatively charged meteor smoke particles.

Approximation of the Mobility of Atomic Ions of Noble Gases in Their Parent Gas

The mobility of ions plays an important role in the theoretical analysis of many phenomena in low-temperature plasmas, such as ambipolar diffusion, the formation of electrode and surface sheaths in gas discharges, particle charging and the ion drag force in dusty plasmas. A modification of the semiempirical Frost formula for the mobility of positive atomic ions in their parent gases is proposed. The modified expression demonstrates excellent agreement with experimental results for various ionized rare gases in a very wide range of electric field strengths and temperatures.

The photon‐ion merged‐beams experiment PIPE at PETRA III—The first five years

The Photon‐Ion Spectrometer at PETRA III—in short, PIPE—is a permanently installed user facility at the "Variable Polarization XUV Beamline" P04 of the synchrotron light source PETRA III operated by DESY in Hamburg, Germany. The careful design of the PIPE ion‐optics in combination with the record‐high photon flux at P04 has lead to a breakthrough in experimental studies of photon interactions with ionized small quantum systems. This short review provides an overview over the published scientific results from photon‐ion merged‐beams experiments at PIPE that were obtained since the start of P04 operations in 2013. The topics covered comprise photoionization of ions of astrophysical relevance, quantitative studies of multi‐electron processes upon inner‐shell photoexcitation and photoionization of negative and positive atomic ions, precision spectroscopy of photoionization resonances, photoionization and photofragmentation of molecular ions, and of endohedral fullerene ions.

Cyclotron transitions of bound ions

A charged particle in a magnetic field possesses discrete energy levels associated with particle rotation around the field lines. The radiative transitions between these levels are the well-known cyclotron transitions. We show that a bound complex of particles with a nonzero net charge displays analogous transitions between the states of confined motion of the entire complex in the field. The latter bound-ion cyclotron transitions are affected by a coupling between the collective and internal motions of the complex and, as a result, differ from the transitions of a ``reference'' bare ion with the same mass and charge. We analyze the cyclotron transitions for complex ions by including the coupling within a rigorous quantum approach. Particular attention is paid to comparison of the transition energies and oscillator strengths to those of the bare ion. Selection rules based on integrals of collective motion are derived for the bound-ion cyclotron transitions analytically, and the perturbation and coupled-channel approaches are developed to study the transitions quantitatively. Representative examples are considered and discussed for positive and negative atomic and cluster ions.

The cryogenic storage ring CSR for collision experiments with state-controlled and phase-space cooled molecular ion beams

SynopsisThe cryogenic storage ring (CSR) for positive and negative atomic, molecular and cluster ions is starting operation at the Max Planck Institute for Nuclear Physics in Heidelberg.

An efficient extrapolation to the (T)/CBS limit.

We extrapolate to the perturbative triples (T)/complete basis set (CBS) limit using double ζ basis sets without polarization functions (Wesleyan-1-Triples-2ζ or "Wes1T-2Z") and triple ζ basis sets with a single level of polarization functions (Wesleyan-1-Triples-3ζ or "Wes1T-3Z"). These basis sets were optimized for 102 species representing the first two rows of the Periodic Table. The species include the entire set of neutral atoms, positive and negative atomic ions, as well as several homonuclear diatomic molecules, hydrides, rare gas dimers, polar molecules, such as oxides and fluorides, and a few transition states. The extrapolated Wes1T-(2,3)Z triples energies agree with (T)/CBS benchmarks to within ±0.65 mEh, while the rms deviations of comparable model chemistries W1, CBS-APNO, and CBS-QB3 for the same test set are ±0.23 mEh, ±2.37 mEh, and ±5.80 mEh, respectively. The Wes1T-(2,3)Z triples calculation time for the largest hydrocarbon in the G2/97 test set, C6H5Me(+), is reduced by a factor of 25 when compared to W1. The cost-effectiveness of the Wes1T-(2,3)Z extrapolation validates the usefulness of the Wes1T-2Z and Wes1T-3Z basis sets which are now available for a more efficient extrapolation of the (T) component of any composite model chemistry.

CCSD(T)/CBS atomic and molecular benchmarks for H through Ar.

We extrapolate to the coupled cluster single and double excitation and the perturbative triples (CCSD(T))/complete basis set (CBS) limit with a sequence of optimized n-tuple-ζ augmented polarization augmented (nZaPa) basis sets (n = 4, 5, 6, and 7) for 115 species representing the first two rows of the Periodic Table. The species include the entire set of atoms, positive and negative atomic ions, homonuclear diatomic molecules, and hydrides. The benchmark set also includes the rare gas dimers, polar molecules such as oxides and fluorides, and a few transition states for chemical reactions. The CCSD correlation energies agree with available CCSD-F12b/3C(FIX) values to within ±0.18 mEh root-mean-square (rms) deviation. The (T) components agree to within ±0.10 mEh and the total CCSD(T) correlation energies to within ±0.26 mEh or 0.1% rms deviation, which is probably the better measure, since the largest deviation is 0.43 mEh or 0.13%. These CBS limits can now be used as benchmarks to calibrate more approximate calculations using smaller basis sets. The sequence of basis sets provides data on convergence patterns for each component of the correlation energy.

Environment assisted electron capture

Electrons scattering off isolated atoms or positive atomic ions may be captured in the non-resonant photorecombination or resonant dielectronic recombination processes with the excess energy carried off by a photon. We demonstrate that in a medium a new interatomic process becomes important, where in the electron capture by an atom or atomic ion the energy is transferred to a neigbouring species ionising it. We discuss different manifestations of this interatomic Coulombic electron capture and estimate its efficiency for a number of realistic systems.

MP2/CBS atomic and molecular benchmarks for H through Ar

We extrapolate to the MP2/CBS limit with a sequence of optimized n-tuple-zeta augmented polarized basis sets (n=4, 5, 6, and 7) for the entire set of 72 atoms, positive and negative atomic ions, homonuclear diatomic molecules, and hydrides representing the first two rows of the Periodic Table. The second-order correlation energies agree with accurate (+/-0.01 mE(h)) numerical values (He, Be, Ne, Mg, Ar, Zn(+2), and Kr) to within +/-0.1%. These MP2/CBS limits of the 72 species can now be used as benchmarks to calibrate more approximate calculations using smaller basis sets.

Time-of-flight detection of monoatomic ions generated by femtosecond laser ablation from large molecules

Single-shot femtosecond laser ablation (fsLA) was applied to large molecules to analyze elemental composition through out wide range of mass-to-charge ratio. Molecular samples such as Eu-DNA and cosmetic powders were atomized and ionized simultaneously by the single-shot fsLA and positive atomic ions were detected using a reflectron time-of-flight (TOF) mass spectrometer. The ratios among the signal intensity of the detected stable isotopes including 151,153Eu and 182–184,186W were consistent with the respective natural abundances of the isotopes. The results demonstrate the feasibility of the fsLA-TOF method as a high-throughput analytical technique for elemental microanalysis of large molecular samples in small quantities.

Low-energy linear oxygen plasma source

A new version of a constricted plasma source is described, characterized by all metal-ceramic construction, a linear slit exit of 180 mm length, and cw operation (typically 50 kHz) at an average power of 1.5 kW. The plasma source is here operated with oxygen gas, producing streaming plasma that contains mainly positive molecular and atomic ions, and to a much lesser degree, negative ions. The maximum total ion current obtained was about 0.5 A. The fraction of atomic ions reached more than 10% of all ions when the flow rate was less then 10 SCCM O(2), corresponding to a chamber pressure of about 0.5 Pa for the selected pumping speed. The energy distribution functions of the different ion species were measured with a combined mass spectrometer and energy analyzer. The time-averaged distribution functions were broad and ranged from about 30 to 90 eV at 200 kHz and higher frequencies, while they were only several eV broad at 50 kHz and lower frequencies, with the maximum located at about 40 eV for the grounded anode case. This maximum was shifted down to about 7 eV when the anode was floating, indicating the important role of the plasma potential for the ion energy for a given substrate potential. The source could be scaled to greater length and may be useful for functionalization of surfaces and plasma-assisted deposition of compound films.

Ionization potentials of neutral atoms and positive ions in the limit of large atomic number

The many-electron Schr\"odinger equation allows one to make predictions for the nonrelativistic ionization potentials of both highly charged positive atomic ions and neutral atoms in the limit of large atomic number $Z$. Beginning with theoretical configuration interaction data on both Li- and Be-like positive atomic ions by K.T. Chung et al. [Phys. Rev. A 45, 7766 (1992); Phys. Rev. A 47, 1740 (1993)], their nonrelativistic first ionization potentials $I$ are plotted in the form of $I∕{Z}^{2}$ versus $1∕Z$. In these two sequences, it is then clear that ${\mathrm{lim}}_{Z\ensuremath{\rightarrow}\ensuremath{\infty}}(I∕{Z}^{2})$ remains finite and that this limit is approached essentially linearly. Interpretation is afforded by means of the so-called $1∕Z$ expansion of atomic theory. The question of the behavior of the nonrelativistic ionization potentials for large $Z$ is then addressed for neutral atoms. We perform density functional theory (DFT) calculations using the local density approximation with Dirac exchange and neglecting Coulomb correlation for the heavy actinides as well as for the rare gas and alkali atoms from $Z=10$ up to $Z=291$. Our results suggest that there is a nonzero value for ${\mathrm{lim}}_{Z\ensuremath{\rightarrow}\ensuremath{\infty}}I$ for both the noble gases and the alkalis, the second one implying that there is a lower bound of about $2.56\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ to the ionization potential of any nonrelativistic neutral atom. We also explore an alternative approach via the one-body potential $V(r)$ of DFT by calculating the eigenenergies of the highest occupied atomic orbital in neutral atoms. Finally, relativistic corrections needed to compare measured ionization potentials to the predictions from the Schr\"odinger equation are briefly considered.

Absolute cross sections for the production of positive atomic ions from dissociative collisions of [formula omitted], [formula omitted] and [formula omitted] in He

Absolute total cross sections are reported for the production of positive atomic ions from dissociative collisions of 1–5keV H3+, D3+ and HD2+ with He for scattering angles up to 5°. The cross sections are of the order of 10−17cm2 for all the processes studied in this work. In order to investigate the mass effect in the dissociation processes, the data are plotted as a function of the projectile speed. The cross sections from HD2+ are normalized to compensate for the relative fragment yield making possible the comparison of the mass effect over the dissociation processes, i.e. 3σ(H+) and 1.5σ(D+) have been considered. For equivelocity incident H3+, D3+ and HD2+, the H+ and D+ formation cross sections were the same within the accuracy of the experiment.

Evidence for Rescattering in Intense, Femtosecond Laser Interactions with a Negative Ion

It is now well established that energetic electron emission, nonsequential ionization, and high harmonic generation, produced during the interaction of intense, femtosecond laser pulses with atoms (and atomic positive ions), can be explained by invoking rescattering of the active electron in the laser field, the so-called rescattering mechanism. In contrast for negative ions, the role of rescattering has not been established experimentally. By irradiating F- ions with ultrashort laser pulses, F+ ion yields as a function of intensity for both linearly and circularly polarized light have been measured. We find that, at intensities well below saturation for F+ production by sequential ionization, there is a small but significant enhancement in the yield for the case of linearly polarized light, providing the first clear experimental evidence for the existence of the rescattering mechanism in negative ions.

Corrections to Slater exchange potential in terms of Dirac idempotent density matrix: With an approximate application to Be-like positive atomic ions for large atomic number

In earlier studies, we have considered the exchange energy density εx(r) in terms of the Dirac density matrix ρ1(r,r′) for the nonrelativistic limit of large atomic number Z in (i) the Be-like series with configuration (1s)2(2s)2 and (ii) the Ne-like series with closed K+L shells. Subsequently the work of Della Sala and Görling [J. Chem. Phys. 115, 5718 (2001)] has appeared, in which an integral equation for the exchange potential vx(r) is given in terms of the idempotent Dirac density matrix, based on the admittedly drastic approximation that the Hartree–Fock and the Kohn–Sham determinants are equal. Here a formally exact generalization of the integral equation is set up and an approximate solution is presented for the Be series at large Z.

Elektronnye protsessy pri medlennom stolknovenii otritsatel'nogo i polozhitel'nogo atomnykh ionov

Elektronnye protsessy pri medlennom stolknovenii otritsatel'nogo i polozhitel'nogo atomnykh ionov

Two-photonexcitation-ionization of the 1s shellof highly charged positive atomic ions

The non-relativistic absolute values and shapes of thecross sections for the process of two-photon one-electronexcitation-ionization of the 1s shell of highly chargedpositive atomic ions Ne6+ and Ne8+ are calculated using second-orderquantum-mechanical perturbation theory, taking intoaccount the many-particle effect of relaxation of the ionresidue in the field of the virtual vacancies created.The many-particle effect of stabilization of the deepvacancy when changing target from the neutral atom to thehighly charged positive ions is also taken into account.The calculations are fulfilled for both linearly andcircularly polarized incident photons.

Electron capture in collisions between negative and positive ions

Collisions between negative and positive atomic ions are investigated. The ionic wave function is expressed in terms of the Coulomb Green’s function. Normalizing this function allows the system of two ions to be described completely. The exchange matrix elements turn out to be the sums of products of the Coulomb wave functions over degenerate states. These sums are expressed in terms of the quadratic form of the wave function for a state with zero angular quantum numbers, l=m=0. The nonadiabatic coupling of quasi-crossing terms with other terms of the system is analyzed; this effect significantly increases the cross section for single-electron capture.

Relative Atomic and Molecular Secondary Ion Yields for SIMS O2+ Analysis of Column 13 Ion Implants in Silicon

SIMS depth profiles for ion implants of column 13 elements in Si have been obtained using O2+ primary beam and detection of positive secondary atomic and molecular ions using high mass resolution. The species monitored were M2+, M+, MO+, M2+, MSi+, and MSiO+, where M is the element of interest.