Jahn-Teller distortion ofC60−in(Ph4As)2

Abstract

We report a combined experimental and theoretical study of the on-ball vibrations of the singly charged C 60 anion. The experimental material is ͑Ph 4 As͒ 2 ClC 60 , a prototypical system for studying isolated C 60 − , which we have investigated by high-resolution infrared spectroscopy in the range 50-1500 cm −1 between 6 and 300 K. Our first-principles quantum molecular dynamics calculations provide complementary information on the vibrational spectra as well as simulated structural information about the reduced-symmetry cage. Our combined results indicate either C 2h or C i symmetry for the Jahn-Teller distorted cage. In both cases, the cage is prolate and elongated along an axis that penetrates opposing five-membered rings. Bond-length changes are less than 0.013 Å. Observed temperature-dependent frequency shifts of the C 60 − vibrations are insufficient to identify any ordering transition, although low-temperature softening of a T 1u ͑4͒-derived mode is substantial.

Vibrational Spectra of C60·C8H8 and C70·C8H8 in the Rotor-stator and Polymer Phases

“…This means that the possible point groups of the C 60 molecules are: Table 5 we show the evolution and splitting of the Raman active A g and H g and the IR active T 1u modes caused by symmetry reduction from I h to these point groups (correlation table). The C 2h and C i point groups can be ruled out because the expected number of additionally activated peaks 25,26 is too high to be reconciled with the observed data. A D 2h distortion could in principle be positively identified as it leads to a threefold splitting of the T 1u modes, in contrast to the others; unfortunately, in this case our fits were not sufficiently robust to distinguish between a three-or twofold splitting.…”

IR spectroscopy of gas-phase C60−

“…The fullerenes in these compounds are well separated from each other and surrounded by PhX + (Ph = phenyl = C 6 H 5 , X = P or As as counterions). 15 In their IR spectra, two resonances at positions similar to those for RbC 60 are observed, with the low frequency mode showing a splitting of about 4 cm À1 (see Table 1). …”

“…However, questions have been raised as to the role of the counter ions, and, in order to minimize their interactions, special compounds have been synthesized and investigated. 15,17,18 C 60 À has also been studied in the gas phase. Using photoelectron spectroscopy, the electron affinity of neutral C 60 is determined to be 2.70 eV.…”

“…6 For C 60 and other fullerenes, this distortion has been investigated both theoretically [6][7][8][9] and experimentally. [10][11][12][13][14][15] Especially C 60 À serves as a model system for the JT effect in highly symmetrical molecules and the molecule is expected to experience a distortion from icosahedral (I h ) to either D 5d or D 3d symmetry. 6 In the solid state, Rb 1 C 60 has been investigated using IR reflectivity measurements.…”

“…In agreement with that, the here presented value for the T 1u (4) of C 60 À is closest to the value reported for solidstate materials which are designed to limit the interactions of C 60 anions with the surroundings. 15 …”