Ions In He Research Articles

Experimental differentiation between electron excitation and electron capture by one electron (F8+) ions in He

The X-ray production cross sections resulting from electron excitation and electron capture of F8+ ions incident on He gas have been measured by observing the X-rays from the 2p to 1s and 1s2p to 1s2 transitions, respectively, over the projectile energy range of 7.5 to 35 MeV. The cross section for electron excitation is approximately constant and becomes dominant over the cross section for electron capture at the highest energies. At the lowest energies, excitation is three orders of magnitude smaller than capture.

Continuous emission in the vacuum ultraviolet under energetic inert gas ion bombardment of aluminium

Collisions of 200-600 keV ions of He, Ne, and Ar with aluminium surfaces have been found to result in the emission of intense continua in the vacuum-UV region. Continua extend from 680 to 990 AA for He, 700-950 AA for Ne and 1095-1425 AA for Ar. The origin of the continuous emission has been interpreted as due to the interaction of accumulated gas atoms in the discrete excited state with identical atoms in their ground state. The spectra result as a consequence of Franck-Condon transitions in the diatomic collision complex.

A note on the structure of positive ions in liquid 4He

Evidence that the positive ion in liquid ^4He forms a solid core with a solid-liquid interface is examined in the light of new analytic solutions to the Navier-Stokes equations. It is found that the existing evidence does not decisively favor the picture that a solid core is formed.

Mobilities and longitudinal diffusion coefficients for Cs+ ions in He and Ne gas

Ion mobilities and longitudinal diffusion coefficients of Cs+ are measured in He and Ne gas using the drift tube mass spectrometer.(AIP)

Motion of positive ions in normal3He

The velocity, v, of positive ions in normal 3He in strong electric fields, E, is calculated using the theory of Fetter and Kurkijarvi (1977). A model for the recoil function, F(k,t), has been proposed by the author, which leads to the prediction that the mobility increases linearly with ln(1/T), where T is the temperature. Measurements of the v-E characteristic will test this model of F(k,t). It is found that the model predicts that v-1=( mu E)-1+C for fields greater than 103 V m-1, a result which has already been observed.

Mobilities of H2O+ and H3O+⋅nH2O (n=0,1,2) ions in He

First Page

Positive ion structure in 3He-rich liquid helium mixtures

The structure of positive ions in impure 3He is investigated. We predict a “halo” of 4He around the ion. We use the halo to interpret recent experiments on ion mobility in 3He. Other properties of the halo are studied.

Positive ion mobility in normal 3He

The mobility of positive ions in pure 3He and in a solution with 300 ppm 4He are reported for a pressure of 60 torr.

Motion of negative ions in superfluid3He

The motion of negative ions in superfluid 3He when acted on by a field is calculated using a model in which the cross-section is taken to be constant. The theory is developed for both the A and B-phase It is argued that the scattering processes can be treated as being elastic for temperatures close to the transition temperature. The theory is in good agreement with experimental results for the B-phase of superfluid 3He for velocities in excess of the critical velocity. It is possible to estimate the energy gap from the data. The theory is not in agreement with experimental results for lower velocities. This implies that the momentum transfer cross-section is smaller than in the normal phase for quasiparticle scattering processes.

The Motion and Mobility of Ions in Superfluid 3He

The mobility of ions in superfluid 3He-B and -A is calculated near the transition temperature and at absolute zero, taking into account the ionic recoil and using the low temperature approximation for the Van Hove scattering function of an ion.

Dissociation and Charge Transfer of CO2 1+ and CO2 2+ Ions in Collisions with Neutral Atoms and Molecules

Abstract Cross sections for single electron capture by CO2 2+ ions as well as total collision cross sections σi,tot (i=1, 2) for CO2 1+ and CO2 2+ ions in He, Ne, Ar, Kr, Xe, H2, O2, N2, CH4 and CO2 gases have been measured at 10 keV impact energy. σ2,1 varies between 4.5·10-17cm2 for the He and 1.8·10·15cm2 for the CO, target. On the average, σ2,1,tot is 1.6 times larger than σ1,tot and shows a nearly linear dependence on the gaskinetic hard sphere cross section of the target particle. The largest observed value of σ2,tot is 9.4·10-15cm2 for the CO2 target.

Mobilities of F−, Cl−, Br−, and I− ions in He

First Page

Monte Carlo simulation of ion motion in drift tubes

The motion of a swarm of ions in a uniform electric field is studied by simulating the motion of a single ion through many collisions with neutral atoms in order to obtain the drift velocity, average energy, and velocity distribution for the ions. For K+ ions in He at low field strengths, the results agree well with the solutions of the Boltzmann equation by Kumar and Robson; and for K+ in Ar at all field strengths, the computed mobilities demonstrate that the Viehland–Mason moment method can give useful results, especially if carried through to third order. The velocity distributions computed for O+ ions in He and Ar are used in the accompanying paper by Albritton et al. to analyze drift tube measurements of O+ reaction rates. Significant deviations from the Maxwell–Boltzmann form have been found and are seen to have important effects in that application. Velocity distributions have also been obtained for Li+ in He. The sensitivity of ionic mobilities to changes in the ion–atom interaction potential is examined with particular reference to K+ ions in Ar.

Mobility of positive ions in normal3He

The mobility of positive ions in liquid 3He is calculated using a modification of the theory of Josephson and Lekner (1969). The mobility is predicted to increase linearly with ln(T0/T) for temperatures between 2 and 50 mK. This is in accord with the experimental results. There is no discontinuity in the mobility according to the theory. It is suggested that the rapid drop in the mobility at 70 mK is caused by 4He atoms condensing on to the surface of the ion, resulting in an increase in the radius of the ion.

Mobilities of Rb+ ions in He, Ne, Ar, H2, N2, O2, and CO2

Mobilities of Rb+ ions in He, Ne, Ar, H2, N2, O2, and CO2

Observation of a second critical field for negative ions in He II

The drift velocity nu of negative ions has been measured in He II near 1K, under a pressure of 25 bar, for electric fields E up to 17 kV cm-1. Beyond Ec1, the critical field for creation of stable charged vortex rings, a second critical field Ec2 has been observed at which nu passes through a minimum and then starts to increase again. Numerical values of the rate nu at which rings are nucleated and of the rate P at which the ions escape from the rings again when E>or=Ec2 are calculated from the experimental data.

Electron capture and loss by ground-state and metastable Li+in helium and argon targets

The initial-growth and beam-attenuation techniques have been used to determine electron-capture cross sections for ground-state Li+ ions, and capture, loss and de-excitation cross sections for metastable Li+ ions in He and Ar. Metastable Li+ ions were produced in collisions between Li2+ ions and Ar in the energy range 40-90 keV, and apparent metastable fractions of about 50% were observed. The electron-loss cross section for metastable Li+ ions is shown to be roughly 50 times larger than the corresponding cross section for ground-state ions. The de-excitation process is believed mainly to be due to electron capture into autoionizing states such as the (1s2s2p)2P state and subsequent decay to the Li+ ground state.

Condensation of isotopic impurities on the negative ion in He II

The authors report experimental evidence that the rate nu at which a negative ion nucleates vortex rings in He II is strongly influenced by 3He isotopic impurity concentrations close to that of the natural abundance. It is suggested that the anomalous temperature dependence of nu observed near 0.3K in earlier experiments in natural 4He is a consequence of 3He condensation on the ions, and that the presence of as few as five condensed atoms is sufficient to completely eliminate the bare ion signal in a typical experimental geometry.

Radiation from a hot, thin plasma from 1 to 250 A

A calculation of emission spectrum of a hot, low-density plasma in the region 1--250 A is presented. The mechanisms considered are electron collision-induced line emission, bremsstrahlung, and radiative recombination; and the temperature range studied is 10/sup 5/--10/sup 7/ K. 795 lines are included. The elemental abundances of the ions of He, C, N, O, Ne, Mg, Si, S, Ca, Fe, and Ni were taken to be as in the solar corona. The line emission of Fe ions produces a maximum in the curve of an emission power between 1 and 250 A versus temperature around 10/sup 6/ K. The emission rate around 10/sup 6/ K is larger than the results calculated by Cox and Tucker and Tucker and Koren. (auth)

Mobility of negative ions in superfluid3He

The mobility of negative ions in superfluid 3He is calculated by making the assumptions that the differential scattering cross section is constant and that the scattering of quasiparticles is elastic. The mobility is anisotropic in the A phase and depends on the angle between the direction of motion and the l vector of the superfluid.