Ions In He Research Articles

Charge Transfer in He+ - He → He(1s4l, l ≥ 2) - He+ Collisions in Intermediate Energy Range.

The anticrossing spectra of the helium line λ1s4l D3,F-1s2p P3=447.2 nm emitted after electron capture by He+ ions in He+-He collisions were measured for projectile energies of 10-29 keV. Furthermore, considering the excited states' time evolution, the theoretical intensity functions were calculated. The electric field and density distributions of the target He atoms in the collision volume were taken into account, and by fitting the theoretical intensities to the measured ones, the post-collisional states of the charge-transferred He atoms were determined. The results indicate that for the intermediate projectile energy range, the electronic charge distributions were asymmetric, but the electric dipole moments did not change, as in the case of the target atoms excited directly in the collisions. This result shows that the Paul trap mechanism may play an important role in the charge transfer excitation in this energy range.

Monte Carlo simulation of O2− ion transport and rate properties in noble gases with O2 addition

The kinetics of O2− ions were numerically studied in He and Ar with a small admixture of O2 in a strong electric field through a Monte Carlo simulation. Cross sections for elastic scattering between O2− ions and He and Ar atoms were determined by adjusting cross section values to obtain good agreement between calculated and measured ion mobilities in pure helium and argon. Ion transport coefficients, mean energy, and detachment rate were calculated for various mole fractions of O2 and values of the reduced electric field. It was shown that the O2− ion mobility, mean energy, and detachment rate in He:O2 mixtures are much higher than those in Ar:O2 mixtures and air. A great difference between the properties of O2− ions in He–O2 and Ar–O2 mixtures was explained on the basis of the difference in the polarizability and mass for He and Ar atoms. Calculated detachment rates can be used for simulating guided ionization waves in He and Ar flows ejected into ambient air.

Kinetics of reactions of NH4 + with some biogenic organic molecules and monoterpenes in helium and nitrogen carrier gases: A potential reagent ion for selected ion flow tube mass spectrometry.

To assess the suitability of NH4 + as a reagent ion for trace gas analysis by selected ion flow tube mass spectrometry, SIFT-MS, its ion chemistry must be understood. Thus, rate coefficients and product ions for its reactions with typical biogenic molecules and monoterpenes need to be experimentally determined in both helium, He, and nitrogen, N2 , carrier gases. NH4 + and H3 O+ were generated in a microwave gas discharge through an NH3 and H2 O vapour mixture and, after m/z selection, injected into He and N2 carrier gas. Using the conventional SIFT method, NH4 + reactions were then studied with M, the biogenic molecules acetone, 1-propanol, 2-butenal, trans-2-heptenal, heptanal, 2-heptanone, 2,3-heptanedione and 15 monoterpene isomers to obtain rate coefficients, k, and product ion branching ratios. Polarisabilities and dipole moments of the reactant molecules and the enthalpy changes in proton transfer reactions were calculated using density functional theory. The k values for the reactions of the biogenic molecules were invariably faster in N2 than in He but similar in both bath gases for the monoterpenes. Adducts NH4 + M were the dominant product ions in He and N2 for the biogenic molecules, whereas both MH+ and NH4 + M product ions were observed in the monoterpene reactions; the monoterpene ratio correlating (R2 =0.7) with the proton affinity, PA, of the monoterpene molecule as calculated. The data indicate that this adduct ion formation is the result of bimolecular rather than termolecular association. NH4 + can be a useful reagent ion for SIFT-MS analyses of molecules with PA(M) < PA(NH3 ) when the dominant single product ion is the adduct NH4 + M. For molecules with PA(M) > PA(NH3 ), such as monoterpenes, both MH+ and NH4 + M ions are likely products, which must be determined along with k by experiment.

Charge transfer and excitation processes in low energy collisions of He+ ions with Li atoms

Electron capture between solar wind ions and neutral species has contributed to the understanding of X-ray production from solar system bodies. The charge transfer and excitation processes in solar wind ions of He+(1s) colliding with Li(1s 22s) atoms are studied by utilizing the full quantum-mechanical molecular-orbital close-coupling (QMOCC) method with impact energies of 0.003–2 keV amu−1. Comparisons of cross sections from single- and multi-configurational calculations for a self-consistent field (SCF and MCSCF) process are carried out. Results show that the dominant reaction channels are He(1s2l 1,3L) + Li+(1s 2 1S). Good consistency is found among present total and state-selective charge transfer and excitation cross sections with other theoretical and experimental data in the same energy region. Due to the differences between coupling matrix elements in high-energy states, the charge transfer cross sections calculated from SCF and MCSCF split slightly as E > 0.4 keV amu−1. Weak Stueckelberg oscillations for charge transfer appear in the present work. In addition, the differences of cross sections for electron excitation to Li(1s 22p) in the singlet/triplet molecular states with He+(1s) are much smaller than those of charge transfer processes because of the similar energy gaps from Li(1s 22p) to the ground state in singlet/triplet states in the large R region.

Mobility of the Singly-Charged Lanthanide and Actinide Cations: Trends and Perspectives.

The current status of gaseous transport studies of the singly-charged lanthanide and actinide ions is reviewed in light of potential applications to superheavy ions. The measurements and calculations for the mobility of lanthanide ions in He and Ar agree well, and they are remarkably sensitive to the electronic configuration of the ion, namely, whether the outer electronic shells are 6s, 5d6s or 6s2. The previous theoretical work is extended here to ions of the actinide family with zero electron orbital momentum: Ac+ (7s2, 1S), Am+ (5f77s 9S°), Cm+ (5f77s2 8S°), No+ (5f147s 2S), and Lr+ (5f147s2 1S). The calculations reveal large systematic differences in the mobilities of the 7s and 7s2 groups of ions and other similarities with their lanthanide analogs. The correlation of ion-neutral interaction potentials and mobility variations with spatial parameters of the electron distributions in the bare ions is explored through the ionic radii concept. While the qualitative trends found for interaction potentials and mobilities render them appealing for superheavy ion research, lack of experimental data and limitations of the scalar relativistic ab initio approaches in use make further efforts necessary to bring the transport measurements into the inventory of techniques operating in “one atom at a time” mode.

Determination of mobility and diffusion coefficients of Ar+ and Ar2+ ions in argon gas

It has recently been shown that accurate theoretical calculations can be used to calibrate a drift-tube mass spectrometer (DTMS) to measure gaseous ion mobilities accurate to within 0.6%. Here we present a new method for calibrating a DTMS instrument to obtain diffusion coefficients parallel to the electric field which are accurate to within 8%. This method is developed and verified by consideration of He+ (2S1/2) ions in He. We apply these techniques to determine transport coefficients for Ar+(2P3/2) and Ar2+ (3P2,1,0) ions in Ar gas at 300 K, with results given as a function of E/N, the ratio of electrostatic field strength to gas number density, in the range 30–210 Td. The measured mobilities are accurate within 0.8%; for Ar+ they agree within 1.5% with Monte Carlo simulations, and for both the cations and dications they are in excellent agreement with previous measurements. Our method gives new diffusion coefficients that agree within 5% with quantum Monte Carlo calculations.

Comparison of isomeric C3H7O+ ion mobilities using fragment ions from 2-butanol and tert-butanol in He and Ne

Mobilities of C3H7O+ ions in He and Ne gas were measured at 85 K and room temperature using a low-temperature drift tube. The effects of structural isomerism on mobility were investigated by comparing C3H7O+ fragments generated by electron impact from 2-butanol ((s)-C3H7O+) and tert-butanol ((t)-C3H7O+). In He at 85 K, the mobility of (t)-C3H7O+ was about 5% less than that of (s)-C3H7O+. Furthermore, to investigate the effects of polarized interactions on ionic structural isomers, measurements in He and Ne buffer gases were compared. The mobilities in Ne were the same at all the tested temperatures.

Core-shell quantum dot electron bubbles as exotic ions in superfluid liquid 4He

A number of experiments in superfluid helium-4 over the past fifty years on the mobility of electron bubbles, which are unique quantum dots in the liquid state, revealed the existence of a “fast” ion and other “exotic” negative ions whose origin and structure still remains unresolved. The fast ion has a mobility which is six times that of the well understood single electron bubble and the other ions span a region from the fast ion mobility to that of the electron bubble. The work presented here shows that a net anionic, two electron, core-shell quantum dot could potentially explain these findings and provide direction for new experimental work. The model described is based on the quantum confinement and stabilization of short-lived shape resonances which originate from anti-bonding orbitals.

Plasma-induced formation of hydrogen resistant oxide layers on zirconium surface

Features of plasma-induced formation of the surface oxide layers on zirconium alloy E110 (Zr–1%Nb) as well as hydrogen resistant properties of these layers are studied. It is shown that irradiation of the E110 sample with 1 keV ions of He + O2 plasma produces the oxide layer depleted by oxygen nearby the surface. The onset of the intensive hydrogen penetration into the ion-irradiated sample during the steam test (673 K, 0.1 MPa) appears to occur 1500 hours later than into the untreated one.

Ab initio study of the mobility of Gd+ ions in He and Ar gases

The mobility of ground-state Gd+ ions in He and Ar gases is addressed theoretically to bridge the surprising gap between the experimental and previous theoretical data. An accurate ab initio coupled cluster approach is used to compute scalar-relativistic interaction potentials for all the molecular states of the Gd+-He and Gd+-Ar pairs. Then a multireference configuration interaction method is used to account for the spin-orbit coupling between the states. This greatly improves the theoretical mobility values at low fields for the 156Gd+(4f75d6s 10Do5/2) ion, bringing them in close agreement with the room-temperature measurements. Several approximations to transport cross sections for the multistate open-shell collisions are assessed and discussed. Accurate description of the transport properties of the heavy open-shell ions is shown to require a demanding high-level ab initio approach. Temperature- or field-dependent mobility data are needed for a more in-depth assessment of the ab initio interaction potentials and dynamic approximations to the cross sections for open-shell ions.

Effects of secondary electron emission on plasma characteristics in dual-frequency atmospheric pressure helium discharge by fluid modeling**Project supported by the National Natural Science Foundation of China (Grant No. 11505089).

A one-dimensional (1D) fluid simulation of dual frequency discharge in helium gas at atmospheric pressure is carried out to investigate the role of the secondary electron emission on the surfaces of the electrodes. In the simulation, electrons, ions of He+ and , metastable atoms of He* and metastable molecules of are included. It is found that the secondary electron emission coefficient significantly influences plasma density and electric field as well as electron heating mechanisms and ionization rate. The particle densities increase with increasing SEE coefficient from 0 to 0.3 as well as the sheathʼs electric field and electron source. Moreover, the SEE coefficient also influences the electron heating mechanism and electron power dissipation in the plasma and both of them increase with increasing SEE coefficient within the range from 0 to 0.3 as a result of increasing of electron density.

Study on changes in structural properties of Ni/Cu dendrites under irradiation by He-particles

Structure and morphology is the basis for the development of functional nanomaterials with controlled properties for practical use. This work is aimed at studying the effect of irradiation with alpha particles on structural and conductive properties of Ni/Cu dendrites. Low-energy ions of He are selected to simulate the accumulation of transmutant helium, leading to swelling and defect formation in the structure, which can lead to a decrease in the operability of electronic devices. In the course of the study, doses were determined in which defects formed during irradiation lead to a decrease in operational characteristics of nanostructures.

Effect of Elastic Collisions on the Ion Distribution Function in Parent Gas Discharge Plasma

An analytical solution is obtained for the Boltzmann kinetic equation for ions in the plasma of its gas with allowance for the processes of resonant charge exchange and elastic ion scattering on the atom. The cross section of differential elastic scattering was assumed to be isotropic in the system of the mass center, and the resonant charge exchange process is independent of the elastic scattering. It is shown that the ion velocity distribution function is determined by two parameters and differs significantly from the Maxwellian one. The allowance for elastic scattering with these assumptions leads to a change in the ion angular distribution and also to a decrease in the average ion energy due to the transfer of part of the ion energy to atoms upon elastic collisions. The calculated values of the drift velocity, the average energy, and the coefficient of transverse diffusion of He+ ions in He, Ar+ ions in Ar are compared with the known experimental data and the results of Monte Carlo calculations; they show good agreement.

Determination of Anisotropic Ion Velocity Distribution Function in Intrinsic Gas Plasma. Theory.

The first seven coefficients of the expansion of the energy and angular distribution functions in Legendre polynomials for Hg+ ions in Hg vapor plasma with the parameter E/P ≈ 400 V/(cm Torr) are measured for the first time using a planar one-sided probe. The analytic solution to the Boltzmann kinetic equation for ions in the plasma of their parent gas is obtained in the conditions when the resonant charge exchange is the predominant process, and ions acquire on their mean free path a velocity much higher than the characteristic velocity of thermal motion of atoms. The presence of an ambipolar field of an arbitrary strength is taken into account. It is shown that the ion velocity distribution function is determined by two parameters and differs substantially from the Maxwellian distribution. Comparison of the results of calculation of the drift velocity of He+ ions in He, Ar+ in Ar, and Hg+ in Hg with the available experimental data shows their conformity. The results of the calculation of the ion distribution function correctly describe the experimental data obtained from its measurement. Analysis of the result shows that in spite of the presence of the strong field, the ion velocity distribution functions are isotropic for ion velocities lower than the average thermal velocity of atoms. With increasing ion velocity, the distribution becomes more and more extended in the direction of the electric field.

Spectroscopy of Ba+ ions in liquid 4He

Atomic ions and free electrons embedded in condensed helium play important role in modern research on quantum fluids and solids. Here we present experimental and theoretical study of Ba+ cations immersed in superfluid He. We observe laser-induced fluorescence of Ba+ injected into liquid He from the plasma of radio frequency discharge in He-Ba gas mixture. The structure of trapping site is studied theoretically in the frame of the atomic bubble model making use of ab initio Ba+ - He pair potentials available in the literature. Calculated spectra of the ion are compared with the results of the experiment.

Illumination of the Earth’s ionosphere by the vacuum ultraviolet radiation reflected by the moon

The spectral curve of the flux density of the radiation, which is reflected by the full moon towards the Earth’s ionosphere within a wavelength range of 200–1700 A, has been presented. This curve is obtained by the approximation of space experiment data available in the scientific literature on the lunar spectral albedo and solar spectrum. Estimates of maximum values of spectral densities of fluxes reflected by the full moon in the neighborhood of wavelengths of ionization of basic ionospheric particles (neutral atoms of H I, He I, N I, O I, and Ar I and ions of He II, N II, O II, Ar II, N III, O III, and Ar III, as well as molecules of H2, N2, and O2) are given.

Friction and Structural Responses of Ion Implanted Polyoxymethylene Copolymer (POM-C)

Polyoxymethylene copolymer (POM-C) round block was implanted with 120 KeV ions of He to doses of 5 x 1016 and 1 x 1016 ions cm-2. It was also implanted with 120 KeV ions of Ar + He and He + Ne to dose of 1 x 1016 ions cm-2, respectively. The friction coefficient behavior of both implanted and unimplanted POM-C blocks was investigated using a ball on disk tribometer mechanism. The friction coefficient of He ion implanted POM-C block at a dose of 5 x 1016 ions cm-2 is lowest compared to all unimplanted and others ions doses implanted POM-C blocks. It also shows the moderate surface texturing (atomic rearrangement), lower surface micro-hardness and average surface roughness compared to both unimplanted and other ions doses implanted POM-C blocks due to well adjusted carbonization, cross-linking and ions-target atoms collisions, which is ascertained from SEM-EDS, Raman spectroscopic and surface profiling observations. The other ions doses implanted POM-C blocks demonstrate the higher friction coefficient and surface roughness with polymer surface deformation (crazing, cracking, pitting and gas evolution, bond breaking) due to severe chain scission, surface dose delivered atomic displacements and chemical structural degradation. It is concluded that the variation in friction coefficient behavior of POM-C block resulted from its structural response for ion beam implantation on the top surface.

Experimental and theoretical determination of the strongly anisotropic velocity distribution functions of ions in the intrinsic gas plasma in strong fields

The first seven coefficient of expansion of the energy and angular distribution functions in the Legendre polynomials for Hg+ ions in the Hg vapor plasma with parameter E/P ≈ 400 V/(cm Torr) are measured for the first time using a planar one-sided probe. The analytic solution to the Boltzmann kinetic equation for ions in the plasma of their parent gas is obtained in the conditions when the resonant charge exchange is the predominant process, and an ion acquires on its mean free path a velocity much higher than the characteristic velocity of thermal motion of atoms. The presence of an ambipolar field of an arbitrary strength is taken into account. It is shown that the ion velocity distribution function is determined by two parameters and differs substantially from the Maxwellian distribution. Comparison of the results of calculation of the drift velocity of He+ ions in He, Ar+ in Ar, and Hg+ in Hg with the available experimental data shows their conformity. The results of calculation of the ion distribution function correctly describe the experimental data on its measurement. Analysis of the result shows that in spite of the presence of the strong field, the ion velocity distribution functions are isotropic for ion velocities lower than the average thermal velocity of atoms. With increasing ion velocity, the distribution becomes more and more extended in the direction of the electric field.

Stark broadening of Xe viii spectral lines

Using the semiclassical perturbation method, we consider, for nine Ar VIII transitions, widths and shifts of spectral lines that are due to collisions with electrons, protons, and ions of He III ut a perturbing particle density of 1018 cm−3 and temperatures between 200,000 and 3,000,000 K.

Gas molecule scattering & ion mobility measurements for organic macro-ions in He versus N2 environments.

A pending issue in linking ion mobility measurements to ion structures is that the collisional cross section (CCS, the measured structural parameter in ion mobility spectrometry) of an ion is strongly dependent upon the manner in which gas molecules effectively impinge on and are reemitted from ion surfaces (when modeling ions as fixed structures). To directly examine the gas molecule impingement and reemission processes and their influence, we measured the CCSs of positively charged ions of room temperature ionic liquids 1-ethyl-3-methylimidazolium dicyanamide (EMIM-N(CN)2) and 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIM-BF4) in N2 using a differential mobility analyzer-mass spectrometer (DMA-MS) and in He using a drift tube mobility spectrometer-mass spectrometer (DT-MS). Cluster ions, generated via electrosprays, took the form (AB)N(A)z, spanning up to z = 20 and with masses greater than 100 kDa. As confirmed by molecular dynamics simulations, at the measurement temperature (∼300 K), such cluster ions took on globular conformations in the gas phase. Based upon their attained charge levels, in neither He nor N2 did the ion-induced dipole potential significantly influence gas molecule-ion collisions. Therefore, differences in the CCSs measured for ions in the two different gases could be primarily attributed to differences in gas molecule behavior upon collision with ions. Overwhelmingly, by comparison of predicted CCSs with selected input impingement-reemission laws to measurements, we find that in N2, gas molecules collide with ions diffusely--they are reemitted at random angles relative to the gas molecule incoming angle--and inelastically. Meanwhile, in He, gas molecules collide specularly and elastically and are emitted from ion surfaces at determined angles. The results can be rationalized on the basis of the momentum transferred per collision; in the case of He, individual gas molecule collisions minimally perturb the atoms within a cluster ion (internal motion), while in the case of N2, individual gas molecules have sufficiently large momentum to alter the internal motion in organic ions.