Near-infrared photoabsorption by C-60 dianions in a storage ring

U. Kadhane, J. U. Andersen, E. Bonderup, B. Concina, P. Hvelplund, M. -B. Suhr Kirketerp, B. Liu, S. Brondsted Nielsen, S. Panja, J. Rangama, K. Stochkel, S. Tomita, H. Zettergren, K. Hansen, A. E. K. Sunden, Sophie Canton, O. Echt, J. S. Forster

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Abstract

We present a detailed study of the electronic structure and the stability of C-60 dianions in the gas phase. Monoanions were extracted from a plasma source and converted to dianions by electron transfer in a Na vapor cell. The dianions were then stored in an electrostatic ring, and their near-infrared absorption spectrum was measured by observation of laser induced electron detachment. From the time dependence of the detachment after photon absorption, we conclude that the reaction has contributions from both direct electron tunneling to the continuum and vibrationally assisted tunneling after internal conversion. This implies that the height of the Coulomb barrier confining the attached electrons is at least similar to 1.5 eV. For C-60(2-) ions in solution electron spin resonance measurements have indicated a singlet ground state, and from the similarity of the absorption spectra we conclude that also the ground state of isolated C-60(2-) ions is singlet. The observed spectrum corresponds to an electronic transition from a t(1u) lowest unoccupied molecular orbital (LUMO) of C-60 to the t(1g) LUMO+1 level. The electronic levels of the dianion are split due to Jahn-Teller coupling to quadrupole deformations of the molecule, and a main absorption band at 10723 cm(-1) corresponds to a transition between the Jahn-Teller ground states. Also transitions from pseudorotational states with 200 cm(-1) and (probably) 420 cm(-1) excitation are observed. We argue that a very broad absorption band from about 11 500 cm(-1) to 13 500 cm(-1) consists of transitions to so-called cone states, which are Jahn-Teller states on a higher potential-energy surface, stabilized by a pseudorotational angular momentum barrier. A previously observed, high-lying absorption band for C-60(-) may also be a transition to a cone state.
Original languageEnglish
JournalJournal of Chemical Physics
Volume131
Issue number1
DOIs
Publication statusPublished - 2009

Bibliographical note

The information about affiliations in this record was updated in December 2015.
The record was previously connected to the following departments: Chemical Physics (S) (011001060)

Subject classification (UKÄ)

  • Atom and Molecular Physics and Optics

Keywords

  • potential energy surfaces
  • paramagnetic resonance
  • nonradiative transitions
  • Jahn-Teller effect
  • infrared spectra
  • ground states
  • fullerenes
  • charge exchange
  • electron detachment
  • rotational states
  • tunnelling
  • vibrational states

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