Far-infrared study of the Jahn-Teller-distortedC60monoanion inC60

Abstract

We report high-resolution far-infrared transmission measurements on C 60 -tetraphenylphosphoniumiodide as a function of temperature. In the spectral region investigated (20-650 cm Ϫ1 ), we assign intramolecular modes of the C 60 monoanion and identify low-frequency combination modes. The well-known F 1u (1) and F 1u (2) modes are split into doublets at room temperature, indicating a D 5d or D 3d distorted ball. This result is consistent with a dynamic Jahn-Teller effect in the strong-coupling limit or with a static distortion stabilized by low-symmetry perturbations. The appearance of silent odd modes is in keeping with symmetry reduction of the ball, while activation of even modes is attributed to interband electron-phonon coupling and orientational disorder in the fulleride salt. Temperature dependences reveal a weak transition in the region 125-150 K in both C 60 Ϫ and counterion modes, indicating a bulk, rather than solely molecular, effect. Anomalous softening ͑with decreasing temperature͒ in several modes may correlate with the radial character of those vibrations.

Discrete Fulleride Anions and Fullerenium Cations

“…How much of this behavior is maintained in condensed media and whether the predominant distortion in the various ions has D 5d , D 3d , D 2h , or lower symmetry remains to be established. 262 Condensed media can trap "snapshots" of these distortions in discrete fulleride ions revealing intrinsic ellipsoidal excursions from pseudo-O h symmetry, but the observed environmental variations suggest there are many wells on a shallow potential energy surface. The accumulation of more data is necessary to map out this surface.…”

“…A 5-fold broadening of the 1394 cm -1 band relative to C 60 has been reported in phosphonium salts of C 60 -. 261 Broadening, as opposed to distinctive frequency shifts, suggests that the effects of site symmetry differences and Jahn- 262 This paper contains a particularly lucid analysis of the problem of distinguishing dynamic from static Jahn-Teller distortions in the C 60 -ion. The symmetry-lowering effect of C-C bond formation in dimer and polymer phases of RbC 60 has been studied for the two highest frequency modes.…”

Far-infrared vibrational properties of high-pressure high-temperatureC60polymers and theC60Long1, Musfeldt2, Kamarás3 et al. 2000Phys. Rev. BSelf Cite292330View full textAdd to dashboardCite

“…Where interference fringes obscured some low-energy fine structure, we subtracted a fit to the fringes, which consisted of a damped sine curve plus a linear background. 40 In some cases, fringes were reduced by smoothing.…”

“…This weak perturbation approach has been successfully applied to (Ph 4 P) 2 IC 60 , in which the isolated singly charged ball undergoes a Jahn-Teller distortion and the I h C 60 vibrations become narrowly split. 40 On the other hand, this type of model cannot adequately describe the vibrational properties of a strongly distorted ball ͑as in the bonded structures of interest here͒, which may exhibit wide splittings, large energy shifts, and mode mixing. Nevertheless, a review of the group theory will provide a useful introduction to the expected changes in numbers of mode activations and splittings, although it provides no information on the energetics.…”

Ordered low-temperature structure inK4C60detected by infrared spectroscopy

“…The first case should lead to a discontinuity at the transition temperature observable by any spectroscopic method, regardless of the time scale; the second scenario would give different transition temperatures depending on the time scale of the experiment relative to the autocorrelation time of the motions. 27 From the parameters given by Zimmer et al, 19 the autocorrelation time is 33 ns at 200 K and 1 ns at 300 K, which can be regarded as static on the time scale of molecular vibrations. The same calculation for the fast uniaxial rotation gives 71 ns at 200 K and 130 ps at 300 K, still too slow to cause collapsing of infrared lines.…”