Vibrational spectra ofC84isomers

Abstract

The vibrational frequencies of three C84 fullerene isomers are calculated with a tight-binding potential model. The differences between the vibrational properties of these isomers are discussed.Following the breakthrough in producing macroscopic quantities of C6o, ' a number of higher fullerenes have also been recently synthesized.The study of structural and dynamical properties of these higher fullerenes has attracted considerable theoretical as well as experimental interests. Among the higher fullerenes, C84 is one of the more abundant species. Although experimental e8'orts have produced detailed information on the ' C nuclear magnetic-resonance spectrum, infrared (IR) spectrum, and ultraviolet photoemission spectrum of C84, ' ' ' many chemical and physical properties of this molecule remain unclear. Three isomers of C84 with Td, D6I"and helical D2 symmetries first proposed by Fowler have been widely studied ' and the helical D2 isomer was preferred by simple Hiickel theory. However, more recent calculations' ' showed that the helical D2 isomer is, in fact, energetically very unfavorable. In our previous work' based on tight-binding calculations for all 24 isolated-pentagon isomers of C84, ' we found that two isomers with D2 and D2d symmetries are energetically most stable. Moreover, these two isomers are so close in energy and structure that they may form an inseparable mixture in the synthesis of C84. Similar results were also obtained from modified neglect of difFerential overlap calculations' and first-principles total-energy calculations. i4'~6In this paper, we present a study of the vibrational properties of the low-energy Dz and D2d isomers of C84 using a tight-binding potential. We also studied the lessstable helical D2 isomer for comparison. Although several theoretical studies on the vibrational properties of C84 have been reported, " the calculations have been performed for the less-stable T", D6~, and helical D2 geometries and not for the low-energy D2 and D2d structures. The tight-binding (TB) potential model used in the present calculation is taken from the previous work of Xu et al. ' In this model, the total energy contains two terms, of various structural and dynamical properties of carbon fullerenes, including the predictions of low-energy structures of C84 and the study of vibrational properties of 18 C6o.The structures of the two low-energy isomers and the helical D2 isomer of C84 used in the present calculation are shown in Fig. 1. The coordinates of the isomers have been optimized by the tight-binding potential. As one can see from Fig. 1, the two low-energy D2 and D2d isomers are quite spherical while the helical D2 isomer has an elongated shape. It is also interesting to note that the two low-energy isomers can be transformed from one to (a) D2 (b) D2d (c) DZ(Helical) occupied E(Ir, I)= g (P"~II&B(Ir;I)~P")+E"&(Ir,j) . The first term in (I) is the electronic energy calculated by a parametrized TB Hamiltonian HrB(Ir; I), and the second term is a short-ranged repulsive energy. This tight-b...

Isolation and Characterization of the Higher Fullerenes from Carbon Soot

“…The absorptions at 1076, 1127 and a bend at 1184 cm −1 moved toward lower frequency correspond to C 84 . Complete absorption in this significant spectrum indicates the dominant presence of the higher fullerene C 84 in the sixth fraction of pyridine extract (18,21,22).…”

“…The isolated higher fullerenes are significant for further investigations of their physical, chemical and spectroscopic properties, as well as for the numerous possible nanotechnological applications in, for example, electronic and optical devices, solar cells, optical, chemical or acoustic sensors, catalysts, synthesis of diamonds, storage of hydrogen, batteries, superconductors, diagnostic or therapeutic agents, transport of metal atoms or biologically active molecules in vivo (1)(2)(3)(4)(5)(6)(7)(8)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30)(31)(32).…”

Theoretical studies of zirconium and carbon clusters with molecular dynamics simulations

“…In this dissertation, we will present a systematic study of structures of fuUerenes ranging from C20 to Cjoo t)y introducing a novel scheme [47]. Using our new scheme, we not only reproduce aU known fuUerene structures but also successfuUy predicted several other fuUerene structures which were confirmed by experi ments [48,49,50]. By utilizing the tight-binding molecular-dynamic (TBMD) simu lation, we also studied the dynamical behavior of fuUerenes: vibrations [51], thermal disintegration [52] of individual clusters as weU as coUisions between fuUerenes [53].…”

“…It was realized that the high yield of Cgg in the experimental synthesis is not solely due to energy stability, otherwise Cyg should be more abundant than Cgg since it has a larger binding energy per atom [46,108]. In order to explain the high yield of Cgg, one has to invoke kinetic factors and postulate that the CgQ molecule has a high barrier towards both further growth or fragmentation under the experimental conditions [123,50].…”

24 IPR isomers of fullerene C84: Cage deformation as geometrical characteristic of local strains

“…Only 10 out of those IPR isomers were isolated as empty molecules: 4 (D 2d ), 5 (D 2 ), 11 (C 2 ), 16 (C s ), 19 (D 3d ), 22 (D 2 ), 23 (D 2d ), 24 (D 6h ) as well as two not identified isomers with C 2 and C s symmetries [7][8][9][10][11][12][13][14]. According to the numerous quantumchemical calculations, these 10 isomers are the most energetically stable [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29].…”