Berlin 2001 – wissenschaftliches Programm
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AMPD: EPS AMPD
AMPD 1: Sitzung 1
AMPD 1.3: Vortrag
Montag, 2. April 2001, 11:55–12:20, H105
The electronic properties of C60 as obtained from collision experiments — •H. Cederquist1, B.A. Huber2, A. Fardi1, P. Hvelplund3, J. Jensen4, H. Lebius2, H.T. Schmidt1, S. Tomita3, and H. Zettergren1 — 1Stockholm University, Frescativ. 24, S-104 05 Stockholm, Sweden — 2Département de Recherche Fondamentale sur la Matiere Condensée/S12A GIM–Grenoble, 17 rue des Martyrs, F-30854, Grenoble Cedex 9, France — 3Institute of Physics and Astronomy, University of Aarhus, DK-8000 Århus C, Denmark — 4Manne Siegbahn Laboratory, Frescativägen 24, S-104 05 Stockholm, Sweden
The main theme of the present discussion is how various collision experiments may be used to study the electronic response of the C60 molecule. Since the discovery of C60 and the method for its mass production, the molecular properties have been investigated by means of its exposure to photons, electrons, clusters (neutral or charged), and atomic ions of varying charge states and velocities. Issues of particular interest here are the ones about energy transfer (heating), cold electron capture, ionization and fragmentation, and strong electron emission in interactions with slow highly charged ions. A new generalized model for electron transfer between two conducting spheres of arbitrary radii [1] is used as a basis for the discussion of recent experimental results on slow C60q+–C60 [2,3], Cq+–C60 [2], Arq+–C60 [4], Xe30+–C60, and Pb54+–C60 collisions. The difference in the C60 target charge–state distributions for atomic– and C60q+–projectile ions is reproduced by selecting model projectile radii to be very small or equal to the C60 radius (7.2 a0), respectively. Further, this model shows that electrons will be captured to excited states of C602+ in C604+-C60 collisions offering a possible explanation for the observed higher tendency for the projectile– than for the target–C602+ to fragment after two–electron transfer [3].
We discuss the formation of hollow atomic projectiles, which according to the model is completed a few atomic units from the C60–cage surface. Ultra–fast emission of highly excited electrons from the outer projectile shells may thus occur in shake–off like processes as vacant intermediate projectile shells are filled making the net projectile charge negative [4]. We note that this mechanism offers a way to rationalize the observation of strong electron emission [5] during the very short interaction (typically sub–femtosecond) between highly charged ions and C60. We will also discuss experimental evidence for very efficient target carbon K–shell vacancy production in collisions between sufficiently highly charged atomic ions and C60 [4]. Finally we give a very brief progress report from ongoing investigations of the stability of highly charged C60q+.
[1] H. Zettergren, H. Schmidt, S. Tomita, P. Hvelplund, H. Lebius, B. Huber, and H. Cederquist, ECAMP VII postersession (2001).
[2] H. Cederquist, P. Hvelplund, H. Lebius, H.T. Schmidt, S. Tomita, and B.A. Huber, Phys. Rev. A 63 (2001).
[3] H. Lebius, H. Schmidt, S. Tomita, P. Hvelplund, H. Cederquist, and B.A. Huber, Phys. Rev. A to be submitted (2001).
[4] A. Langereis, J. Jensen, A. Fardi, K. Haghighat, H.T. Schmidt, S.H. Schwartz, H. Zettergren, and H. Cederquist, Phys. Rev. A submitted (2001).
[5] S. Martin, L. Chen, A. Denis, and J. Désesquelles, Phys. Rev. A 59, 1734 (1999).