Pinch mode

Two different kinds of composite samples were examined. We call one of them polymeric because optical absorption spectra revealed considerable broadening and blue shift typical for polymerized C6o- Another sign of polymerization is a red shift of 8 cm 1 and broadening of C6o pentagonal pinch mode Ag(2) in Raman spectra. X-ray diffraction patterns of these samples did not show crystalline metal and revealed only some features of amorphous and crystalline C6o- Another kind was obtained for layer-by-layer deposition by alternate opening Sn and C6o shutters the fullerene deposition flux being 10 times less intense. Optical absorption spectra of these samples revealed absence of the main C6o bands. SEM... 

Fig. 10.6 Extrapolation to 0 K of the Cm infrared absorption band position. This is the case of the F (4) band, the pentagonal pinch mode. The intercept at 0 K occurs at 1430.9 cm-1...

Fig. 10. Pentagonal pinch mode of a C60 crystal at different pressures suggesting the formation of an orientational glass (from Chandrabhas et al. [14]).

The Ih symmetry of the 60-atoms molecule allows 2Ag and SH modes to be Raman active and 4T modes to be IR active. The four IR active modes are at 1430, 1185, 580 and 528 cm , respectively. The most important Raman modes are at 1469 (tangential bond alternation or pinch mode, Ag), 495 (radial breathing mode, T ) and 271 (squashing mode, Hg) cm , respectively. In the low temperatur phase degenerate modes split from a crystal field and Davidov interaction. Good reviews on the group theoretical analysis and on the line positions are given in (Dresselhaus et al., 1992 Matus and Kuzmany, 1993). 

Figure 4.8-28 Position and line shape of the Aj,-pinch mode in K vC for various doping states x in single crystal 50 (a) and temperature dependence of the spectra in the corresponding spectral range for x=l. Winter and Kuzmany (1994), unpublished (b), according to Winter and Kuzmany (1994).

Figure 2.47 shows a high-resolution Raman spectrum of the pentagonal pinching mode [Ag 2) of C6o in a frozen solution in CS2 at 30 Kobtained by Guhaetal. [1548]. 

Fig. 2.47. Unpolarized Raman spectrum of a frozen solution ofCeo in CS2at30 K. The solid line is a 3-Lorentzian fit to the experimental data. The highest frequency is assigned to the totally symmetric pentagonai-pinch Ag mode in The other two lines are assigned to the pentagonal-pinch mode in molecules containing one and two isotopes, respectively. The inset shows the evolution of these peaks as the solution is warmed [1548].

The intensity of the Ag pentagonal pinch mode which appears at 1468 cm"1 in the Raman spectra of pristine C6o is very sensitive to the presence of polymerized fullerene phases [1]. Raman spectra of the fullerene composite membranes (d - 0.5 pm) shown in Fig. 1 were obtained in the vicinity of this Ag mode (1468 cm 1) before and after the ozone treatment. The ozone treatment of the both nonpolymerized and polimerized fullerene films did not result in a... 

Finally, an interesting comparison can be performed between the influence of the charge transfer on the pinch mode in the doped fullerenes and its influence on the C=C stretching mode in conventional charge transfer systems (Figure 12). For the fulle-... 

Figure 12. Shift of mode frequency i/ as a function of charge transfer x for the pinch mode in Cso (a) and for the C=C stretch mode in the TCNQ molecule of NMPj,Phen(i j.)TCNQ...

Figure 1.10 Raman pentagonal pinch mode of a Cgo single crystal underpressure showing pressure-induced broadening due to the possible formation of an orientational glass. (From Chandrabhas, N. et al., Chem. Phys. Lett., 197, 319, 1992. With permission.)... 

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