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

Artikel i vetenskaplig tidskrift
Författare 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
Klavs Hansen
Erika Sundén
S. E. Canton
O. Echt
J. S. Forster
Publicerad i JOURNAL OF CHEMICAL PHYSICS
Volym 131
Nummer/häfte 1
ISSN 0021-9606
Publiceringsår 2009
Publicerad vid Institutionen för fysik (GU)
Språk en
Länkar dx.doi.org/10.1063/1.3149775
Ämnesord fulleride anions, spectra, superconductivity, spectroscopy, transitions
Ämneskategorier Atom- och molekylfysik och optik

Sammanfattning

We have made a detailed study of the electronic structure and the stability of C60 dianions in the gas phase. Monoanions have been extracted from a plasma source and converted to dianions by electron transfer in a Na vapor cell. The dianions were 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 decay after photon absorption we conclude that the detachment 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 second attached electron is at least 1.5 eV. The observed spectrum corresponds to an electronic transition from a t1u LUMO of C60 to the t1g 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 pseudo–rotational states with 200 cm−1 and (probably) 420 cm−1 excitation are observed. We argue that a very broad absorption band, from about 11500 cm−1 to 13500 cm−1, consists of transitions to so–called cone states, which are Jahn–Teller states on a higher potential– energy surface, stabilized by a pseudo–rotational angular momentum barrier. A previously observed, high-lying absorption band for C−60 may also be a transition to a cone state. For C2− 60 ions in solution ESR measurements have indicated a singlet ground state, and from the similarity of the absorption spectra we conclude that also the ground state of isolated C2− 60 ions is singlet.

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