Infrared intramolecular vibrations and lattice modes in the crystalline phase of 2,2'-bithiophene (2T) are investigated using the direct method combined with density functional theory (DFT)-based total energy calculations. For the first time, the far- and mid-infrared responses have been calculated from the Gamma-point modes and the Born effective charge tensors of the 2T crystalline phase. The relative good agreement between the calculated and experimental infrared spectra allows us to assign the origin of the main features of the experimental spectra, which is of particular interest in the far-infrared domain. These assignments are useful for understanding all the properties of the 2T crystalline phase in which phonon-phonon and electronphonon interactions play an important role.

Phonons in the α-quaterthiophene (4T) and α-sexithiophene (6T) polymorph phases are investigated using the direct method combined with density functional theory (DFT)-based total energy calculations. The simulation of inelastic neutron scattering spectra (INS) on the LT and HT polymorph phases of 4T and 6T enable the corresponding spectral signatures of these materials to be identified. In particular, there are two fingerprints: (i) the low-frequency vibrational modes (frequencies lower than 200 cm(-1)) and (ii) the vibrational modes in the 600-900 cm(-1) frequency range. The good agreement with the INS experimental data allows us to assign unambiguously the origin of all features (first-order and high-order processes) of these spectra and to predict that the LT phase is the phase measured experimentally both on the 4T and 6T materials. Moreover, the broad background in the 600-1400 cm(-1) frequency range and the well-defined features which appear around 940 cm(-1) in the calculated INS spectra of 4T/HT and 6T/HT are assigned to multiphonon contributions. This multiphonon contribution at 940 cm(-1), which is absent in the 4T/LT and 6T/LT INS spectra, also constitutes a fingerprint of the HT phases. Finally, the calculated dispersion curves of the two polymorph phases of 4T and 6T are given.

The local structure around the rubidium ions inserted in single-wall carbon nanotube bundles (Rb-doped SWCNT) is studied by Rb K-edge extended x-ray-absorption fine structure (EXAFS). The dependence of the local order around the rubidium ions is investigated as a function of the time of doping (i.e., as a function of the stoichiometry of the sample). The first coordination shell of the rubidium ions, related to the distance between rubidium and the first nearest-neighboring carbon atoms, has a clear time doping dependence. Comparison between ab initio simulations of the EXAFS spectra and experimental data questions the interstitial site (between three tubes) as the preferential insertion site in SWCNT bundles. The results indicate that the rubidium ions are mainly located inside the tubes and around the bundles. The results are in good agreement with combined x-ray and neutron diffraction experiments performed on the same samples.

Inelastic neutron scattering investigations of the orthorhombic (O), tetragonal (T), and rhomboliedral (R) pressure-polymerized phases of C-60 as well as the pressure-dimerized state give evidence for differences in the responses of low-energy excitations between these phases. These differences are assigned to changes in low-energy interball modes dynamics as a function of the structure of pressure-polyutmerized phases. Far-infrared transmittance measurements complete the information of the low-frequency vibrational dynamics of these phases. The temperature dependence of these low-frequency excitations reveals a strong anharmonicity and possible phase transitions.