Experimental and model angular distributions of one- and two-electron capture processes in 0.5–20 eV/u<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msup><mml:mrow><mml:mi mathvariant="normal">Ar</mml:mi></mml:mrow><mml:mrow><mml:mn>4</mml:mn><mml:mo>+</mml:mo></mml:mrow></mml:msup></mml:mrow></mml:math>-Ar collisions

Biedermann, C.; Cederquist, H.; Andersson, L. R.; Levin, J. C.; Short, R.T.; Elston, S. B.; Gibbons, J. P.; Andersson, H.; Liljeby, L.; Sellin, I. A.

doi:10.1103/physreva.41.5889

Cited by 33 publications

(10 citation statements)

References 39 publications

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“…As pointed out, experimental information [6][7][8][9][10] suggest that the two first steps in (1) and (2) are identical and hence F can be written…”

Section: E Q+ + B--+xe(q-~)+(nl) + B + Xe(~-e)+(nl N't ') + B 2+mentioning

confidence: 99%

“…As indicated by (1), the two-electron transfer process proceeds through two consecutive one-electron transitions. It has been shown through numerous experimental studies of projectile scattering angles that such two-step processes dominate for collision systems where the densities of projectile capture states are sufficiently high [8][9][10].The electric dipole decay rate scales as q4 while the Coulombic autolonlzation rate is independent of q. Since a typical allowed radiative decay rate is about four orders of magnitude smaller than a typical autoionization rate in a neutral atom, one would expect that the two decay branches will be of equal importance for projectile charge states in the vicinity of q=lO [11].…”

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confidence: 99%

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Radiative stabilization following transfer of two electrons to Xe q+ (q ≤ 35) in slow collisions with He and Xe

Cederquist¹

1991

Z Phys D - Atoms, Molecules and Clusters

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We present a derivation of an ECB-based relation between the branching ratio for autoionization F and the ratio between the cross sections for transfer ionization and single-electron capture. We apply this method to two different experimental results. The method yields semi-empirical upper limits for F of unity for double R.ydberg levels formed in Xeq+-He collisions for charge states up to q=29. The fact that direct measurements of aTl/(CrTi+aDC ) leads to values in the range 0.925. We point out that the apparent discrepancy between the results obtained for He and Xe targets at high q could be explained by population of higher angular momentum (1, I r) states in the latter case. I. I n t r o d u c t i o nIn this paper we will present experimental results on branching ratios for autoionization, F, for doubly excited states of Xe (q-2)+ populated through two-electron transfer in Xeq+-He collisions at 4q keV [1]. We will also review earlier results for semi-empirical upper limits of F for double Rydberg states formed in 4q keV Xeq+-Xe collisions [2,3]. The latter results are obtained using the extended classical over barrier (ECB) model [4,5] and measured ratios between the cross sections for transfer ionization and single-electron capture, R [2,3]. In the present energy regime, where the collision velocity is much lower than the orbital velocities of active electrons (v<< 1 a.u.), transfer ionization has been found to proceed through the formation of an intermediate doubly excited state (nl, n'l') which autoionizes at large internuclear separations [6,7]: X e q+ + B--+Xe(q-~)+(nl) + B + Xe(~-e)+(nl, n't ') + B 2+,Xe (q-~)+ + B 2+ + e-. (1) Here (n, n') and (l, l') denote the principal and angular momentum quantum numbers of the two transferred electrons, respectively, while B represents the target species. As indicated by (1), the two-electron transfer process proceeds through two consecutive one-electron transitions. It has been shown through numerous experimental studies of projectile scattering angles that such two-step processes dominate for collision systems where the densities of projectile capture states are sufficiently high [8][9][10].The electric dipole decay rate scales as q4 while the Coulombic autolonlzation rate is independent of q. Since a typical allowed radiative decay rate is about four orders of magnitude smaller than a typical autoionization rate in a neutral atom, one would expect that the two decay branches will be of equal importance for projectile charge states in the vicinity of q=lO [11]. This prediction is, however, partly contradicted by calculations by Hansen [12], who found that autoionization dominates the decay of doubly excited Ar 14+ states due to the possibility of low-energy electron em...

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“…As pointed out, experimental information [6][7][8][9][10] suggest that the two first steps in (1) and (2) are identical and hence F can be written…”

Section: E Q+ + B--+xe(q-~)+(nl) + B + Xe(~-e)+(nl N't ') + B 2+mentioning

confidence: 99%

mentioning

confidence: 99%

Radiative stabilization following transfer of two electrons to Xe q+ (q ≤ 35) in slow collisions with He and Xe

Cederquist¹

1991

Z Phys D - Atoms, Molecules and Clusters

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“…The experimental apparatus, in its different stages of development, has been described before [8,20,21]. Here we restrict ourselves to a brief presentation of its most essential components.…”

Section: Experimental Technique and Data Analysismentioning

confidence: 99%

Angular distributions for single- and double-electron capture in slowC4+-Ne collisions

et al. 1994

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In an earlier experiment by H. Cederquist et al. [J. Phys. 8 18, 3951 (1985)] an unusual Q-value distribution for true double-electron capture was reported for 400-eV C +-Ne collisions: strong population of reaction channels resulting in Q values between 27 and 35 eV followed by weakly populated channels in the region 18 -25 eV and then again a strong channel at Q=16 eV. The last channel is nearly degenerate in Q value with the dominant single-electron capture reaction. Here, we report measured angular distributions for scattered projectiles in single-and double-electron capture at collision energies 0.6 -1.0 keV. At 0.6 keV both single-and double-electron capture exhibit strong forward peaks for Q 16 eV. The intensity for the latter, but not the former, decreases drastically when the energy is raised to 1 keV. The energy dependence of the angular distribution for double-electron capture with Q ) 20 eV can be qualitatively understood in simple terms; singleelectron captures to 2s and 2p orbitals, however, yield unexpectedly wide and structured angular distributions.PACS number(s): 34.70.+e, 34.50.Fa

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“…The change in electronic energy, or Q value, for such a process is a direct measure of the distribution of final states populated on the projectile, which is in turn one of the most crucial tests of any theoretical description of the process. Direct measurement of the energy gain of the projectile has often been used to determine this final-state distribution [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16]. Since the fractional energy resolution practically achievable rarely exceeds 10 ~3, this technique has usually been limited to projectiles of 10 keV and less, and to single and double capture.…”

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Q-value measurements in charge-transfer collisions of highly charged ions with atoms by recoil longitudinal momentum spectroscopy

et al. 1992

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We report on the first (7-value measurements in charge-transfer collisions using recoil longitudinal momentum spectroscopy. This method is not limited to relatively low beam energies and is easily adaptable to captures involving any number of transferred electrons. A very monoenergetic beam is not necessary. For a 50-keV Ar ,5+ on Ar collision system, Q values corresponding to single through quintuple electron capture were measured and found to be in good agreement with the predictions of the molecular classical overbarrier model. PACS numbers: 34.70.+e, 34.50.Fa When a multiply charged ion moving at a velocity below that of typical outer shell atomic electrons encounters a neutral target, the dominant electron removal process is electron capture. The change in electronic energy, or Q value, for such a process is a direct measure of the distribution of final states populated on the projectile, which is in turn one of the most crucial tests of any theoretical description of the process. Direct measurement of the energy gain of the projectile has often been used to determine this final-state distribution [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16]. Since the fractional energy resolution practically achievable rarely exceeds 10 ~3, this technique has usually been limited to projectiles of 10 keV and less, and to single and double capture. For higher energies, measurement of Q through direct energy change of the projectile becomes increasingly more difficult [17]. It has been pointed out previously that recoil ion longitudinal momentum can yield direct information on the Q value and electron mass transfer in fast-ion-atom collisions [18]. In this work we report the first experimental use of recoil longitudinal momentum spectroscopy to obtain Q values for capture. The technique is not limited to collision energies below a few keV, and can be used in situations for which the beam energy is not very well determined. This technique is readily applicable to any charge-transfer number, and is not affected by the kinematic broadening due to autoionization of the projectile following the collision. We apply the method to measure Q values for up to fiveelectron transfer for Ar 15 " 1 " ions on Ar.For collisions involving /-electron capture, conservation of both energy and momentum results in a simple relation between the Q value of the collision and the momentum transfer to the recoil given by (in a.u.)(1) where v is the projectile velocity, P\\ and P± are the longitudinal and transverse (relative to the beam direction) components of the momentum transfer to the recoil, and M\ and Mi are the projectile and recoil masses, respectively. The term iv 2 /2 appears due to the fact that the captured electrons are moving with the projectile at velocity r just after the collision. We will show later that Q' is much smaller than QQ and to a very good approximationsuch that it is sufficient to measure P\\ to obtain Q values. We wish to emphasize that this technique applies only to pure electron capture collisions, and bre...

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Experimental and model angular distributions of one- and two-electron capture processes in 0.5–20 eV/uAr4+-Ar collisions

Cited by 33 publications

References 39 publications

Radiative stabilization following transfer of two electrons to Xe q+ (q ≤ 35) in slow collisions with He and Xe

Radiative stabilization following transfer of two electrons to Xe q+ (q ≤ 35) in slow collisions with He and Xe

Angular distributions for single- and double-electron capture in slowC4+-Ne collisions

Q-value measurements in charge-transfer collisions of highly charged ions with atoms by recoil longitudinal momentum spectroscopy

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