R. Kostić

Vibrational spectroscopy of polypyrrole, theoretical study

Theoretical vibrational spectra of polypyrrole are presented, based on a single‐periodic‐chain model and harmonic potential in‐plane and out‐of‐plane parameters transferred from the pyrrole molecule. The infrared‐absorption intensities were included in the calculations for the first time in polypyrrole. Experimental spectra are analyzed and compared with theoretical ones. Some modes in the experimental spectra indicate the presence of nonplanar conformation. Also, Raman frequencies were compared with experimental ones. Significant effects of electron–phonon coupling are absent.

Cd1-xMnxS Nanoparticles: Far-Infrared Phonon Spectroscopy

Phonon spectra of Cd1-xMnxS (x = 0; 0.01; 0.05; 0.1; 0.15; 0.3) nanoparticles (d ~ 4.5 nm) have been investigated by far-infrared reflection (FIR) (spectral range 40 - 600 cm-1, temperature range 80 – 300 K) and Raman spectroscopy (100 – 700 cm-1, 300 K). Cd1-xMnxS nanoparticles have been synthesized by using aqueous solution precipitation. We obtained interesting features in FIR spectra: there are expected modes of bulk CdS (240 cm-1, 300 cm-1), new modes connected with nano-size of CdS (130 cm-1, 170 cm-1) and additional mode at 120 cm-1 in Cd1-xMnxS nanoparticles which can be assigned to the presence of Mn. The position of obtained modes is discussed in the frame of the linear chain model with both mass and force constant defects. Raman spectroscopy gives us only the mode at 300 cm-1 and its second harmonic.

Infrared spectroscopy and stereochemical structure of poly(P-phenylene vinylene)

Abstract Theoretical infrared (ir) spectra of trans- and cis- forms of poly(p-phenylene vinylene) (PPV) are presented, based on a single-period-chain model and harmonic potential with parameters transferred from p-divinyl benzen molecule. The out-of-plane degrees of freedom and the infrared intensities were included in the calculations. The calculations of polarized infrared spectra of cis- and trans-PPV do not show practically any difference. However, as the calculations evince the absence of the in-plane C-H bending infrared absorption band of trans-vinylene portion of experimental infrared spectrum of PPV, which is a consequence of a delocalized π-electron system (similarly to the case of trans-polyacetylene but not cis-polyacetylene), it seems that stereochemical structure of PPV is of the trans-form. Additional X-ray analysis is still necessary to support our conclusion.

Vibrational Properties and Structure of Carbon Nanotubes Based on C60 Molecule and Its Symmetry

Carbon nanotubes based on molecule C 60 are analysed. These tubes can be considered as an approximation of the smallest possible diameter for carbon fiber. The tubes symmetry is lower than that of the icosahedral C 60 molecule and therefore the infrared- and Raman-active modes are expected to split. We used this symmetry classification to consider the vibrational problem of the grapheme nanotubes as quasi one-dimensional (ID) objects.

Vibrational Cluster Calculations of Zig-Zag Carbon Single-Wall Nanotubes

The results of theoretical cluster calculations of positions of the vibrational IR and Raman active modes of zig-zag carbon single-wall nanotubes of small diameter are presented. These results might be significant for fast diagnostics of the structure of synthesized carbon single-wall nanotubes.

Vibrational spectroscopy and comparative study of trans-polyacetylene, poly(p-phenylene) and poly(p-phenylene vinylene)

Abstract Theoretical vibrational spectra of trans -polyacetylene (PA), poly(p-phenylene) (PPP) and poly(p-phenylene vinylene) (PPV) are presented, based on a single-periodic-chain model and a harmonic potential with parameters transferred from trans -hexatriene, toluene, and p-divinyl benzene, respectively. The out-of-plane degrees of freedom and the infrared absorption intensities were included in the calculations. The calculations evince the absence of the in-plane C-H bending infrared absorption band of the trans -vinylene portion of trans -PA and PPV, which is a consequence of a delocalized π-electron system. The electron-phonon coupling in PPP and PPV is relatively weak - in contrast to trans -PA, where the frequencies of the principal Raman lines are significantly lowered. As a consequence, the PPV is an example of pristine polymer with well delocalized π-electron system, but without significant electron-phonon coupling.