Infrared and Raman evidence for dimers and polymers inRbC60

Abstract

The infrared-and Raman-active vibrational modes of C 60 were measured in the various structural states of Rb 1 C 60 . According to earlier studies, Rb 1 C 60 has an f cc structure at temperatures above ∼ 100 • C, a linear chain polymer orthorhombic structure when slowly cooled, and an as yet undetermined structure when very rapidly cooled ("quenched"). We show that the spectra obtained in the polymer state are consistent with each C 60 molecule having bonds to two diametrically opposite neighbors. In the quenched state, we find evidence for further symmetry breaking, implying a lower symmetry structure than the polymer state. The spectroscopic data of the quenched phase are shown to be consistent with Rb 2 (C 60 ) 2 , a dimerization of C 60 .

Far-infrared study of the Jahn-Teller-distortedC60monoanion inC60Long1, Musfeldt2, Schilder3 et al. 1998Phys. Rev. B255391View full textAdd to dashboardCite

“…In the polymer and dimer phases of the A 1 C 60 compounds, the balls are bonded to one or more of their neighbors, thus reducing the molecular symmetry to D 2h and even lower. [34][35][36] Similar structurally induced symmetry reductions are found in the high-pressure/high-temperature polymerized fullerites, in which the balls remain neutral. 34,37 The hightemperature (Ͼ400 K) fcc A 1 C 60 phase is the most similar to ͑Ph 4 P͒ 2 IC 60 in that both contain the singly charged ball in a very symmetric environment, although the balls separations are quite different.…”

Far-infrared vibrational properties of high-pressure high-temperatureC60polymers and theC60Long1, Musfeldt2, Kamarás3 et al. 2000Phys. Rev. B292330View full textAdd to dashboardCite

“…5,24 We find that features at 509, 517, 526, 541, 554, and 571 cm Ϫ1 also appear in the O-polymer spectrum, but with much weaker intensity than the primary modes we assign. Interestingly, whereas the FIR spectra of the O polymer and RbC 60 differ considerably, the Raman spectra of the two linear polymers were found to be nearly identical.…”

“…1,2 When the weak van der Waals forces among fullerene balls are replaced by different configurations of covalent bonds, the vibrational properties change dramatically. [3][4][5] Both interball interactions and symmetry reductions produced by distortions of the bonded C 60 balls are effectively studied through their effects on the vibrational spectrum.…”

Pressure induced dimerisation of C70

“…Raman modes are also observed in the infrared spectrum and vice versa. In fact such an argument has been used to identify Cm dimer in RblC6,, [25]. To obtain more definitive confirmation on the formation of C70 dimers under HPHT treatment, detailed theoretical analysis of the vibrational spectrum of C70 dimers are called for, as has been done recently [2 1 ] for dimers of C60.…”