Observation of Direct Ionization of He by Highly Charged Ions at Low Velocity

Wu, Wenming; Cocke, C. L.; Giese, J. P.; Melchert, F.; Raphaelian, M. L. A.; Stöckli, M. P.

doi:10.1103/physrevlett.75.1054

Cited by 38 publications

(26 citation statements)

References 22 publications

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“…In the low-to intermediate-energy range, a scaling law has been obtained by Wu et al [24,25] for ionization in collisions of highly charged ions with H and He targets using generalized reduced cross sections σ = σ I 1.3 /q as a function of a reduced collision energy E = E/I q 1/2 . While the energy dependence of the scaled cross sections for the systems studied in the present work are similar to the proposed scaling law, the absolute magnitude is underestimated by almost an order of magnitude.…”

Section: Ionization Of Ground-and Excited-state Sodiummentioning

confidence: 98%

State-selective electron transfer and ionization in collisions of highly charged ions with ground-state Na(3s) and laser-excited Na*(3p)

et al. 2012

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Single electron transfer and ionization in collisions of N 5+ and Ne 8+ with ground state Na(3s) and laser excited Na * (3p) are investigated both experimentally and theoretically at collision energies from 1 to 10 keV/amu, which includes the classical orbital velocity of the valence electron. State-selective partial cross sections are obtained using recoil-ion momentum spectroscopy in combination with a magneto-optically cooled Na atom target. A strong dependence of the cross sections on the collision energy is observed. In general, both the relative magnitude and the energy dependence are found to be in good agreement with classical-trajectory Monte Carlo calculations.

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Section: Ionization Of Ground-and Excited-state Sodiummentioning

confidence: 98%

State-selective electron transfer and ionization in collisions of highly charged ions with ground-state Na(3s) and laser-excited Na*(3p)

et al. 2012

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“…Compared to this capture transition, the emission of an electron into the continuum is extremely unlikely [1]. While in a fast ion collision direct ionization by light projectiles is rather well understood, there has been much discussion of which mechanism promotes electrons into the continuum in slow collisions.…”

mentioning

confidence: 99%

“…In ion-atom collisions, where the velocity of the projectile is much slower than the classical Bohr velocity of the target electrons, the dominant process which ionizes the target is electron capture to bound states of the projectile. Compared to this capture transition, the emission of an electron into the continuum is extremely unlikely [1]. While in a fast ion collision direct ionization by light projectiles is rather well understood, there has been much discussion of which mechanism promotes electrons into the continuum in slow collisions.…”

mentioning

confidence: 99%

Imaging of Saddle Point Electron Emission in Slowp−HeCollisions

Dørner

Khemliche²,

Prior³

et al. 1996

Phys. Rev. Lett.

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100

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The two-dimensional velocity distribution of electrons emitted in 5 -15 keV p-He collisions has been measured for completely determined motion of the nuclei, that is, as a function of the impact parameter and in a well defined scattering plane. The electrons are emitted preferentially in the scattering plane and in the forward direction. The velocity distributions show sharp structures that vary strongly with impact parameter and projectile velocity. The results are compared to classical trajectory calculations. [S0031-9007(96)01614-6] PACS numbers: 34.50.FaIn ion-atom collisions, where the velocity of the projectile is much slower than the classical Bohr velocity of the target electrons, the dominant process which ionizes the target is electron capture to bound states of the projectile. Compared to this capture transition, the emission of an electron into the continuum is extremely unlikely [1]. While in a fast ion collision direct ionization by light projectiles is rather well understood, there has been much discussion of which mechanism promotes electrons into the continuum in slow collisions.On the grounds of classical mechanics, Olson [2] suggested a "saddle point mechanism." The potential between the projectile and the residual target ion has a point (the saddle point) where no force acts on an electron moving between them. As the projectile and target separate, the potential rises and hence electrons traveling with the velocity of this saddle could be "left stranded" in the continuum between the target and projectile [2]. The relative importance of this mechanism has been discussed within the theoretical framework of classical mechanics [2-4] as well as in various quantum mechanical approaches [5][6][7][8][9][10][11][12]. Many experimental studies have sought evidence for it in ionization [3,13-16] and excitation [17,18]. Recently Pieksma and co-workers [19] measured the velocity distribution of electrons emitted in 1-6 keV p-H collisions integrated over all emission angles and found a maximum of the cross section at the velocity of the saddle point. Kravis and co-workers [20] obtained two-dimensional images of the longitudinal and transverse velocity of the continuum electrons, using a technique similar to that used here, but without impact parameter determination, for a wide range of impact velocities of p and C 61 projectiles. Only for proton impact below 1 a.u. (atomic unit velocity) did they find most of the electrons in the saddle point region. Within the hidden crossing theory [9] ionization at these slow velocities has been explained as a multistep promotion process in the quasimolecule formed during the collision, and characteristic electron velocity distributions in the scattering plane have been predicted for a quantum mechanical analog of the classical saddle point mechanism [11,12].In this Letter we present an experimental study of 5-15 keV p-He collisions, which, for the first time give two-dimensional images of the square of the final state electron wave function in velocity space with simul...

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“…As can be seen in Fig. 3, in most of the cases the electron in the quasimolecular orbital is, however, not emitted to the continuum but captured to projectile orbital (see also [140]). Those few electrons released to the continuum are found mostly with very little momentum in between target and projectile frame (see Fig.…”

Section: Slow Collisionsmentioning

confidence: 96%