Polyacetylene Raman

We obtained the true cis -polyacetylene Raman cross-sections, reported in Table 2, by multiplying the integrated observed Raman intensities by these correction factors. Moreover, corrected Raman intensity ratios for the X(YX)Y configuration have been derived for the C-C mode of trans- polyacetylene, which peaks around 1100 cm-i. Given the dispersion of the... 

D. carota ssp. commutatus) were also investigated regarding the accumulation of polyacetylenes. Raman spectra prove that mainly falcarindiol is present in the individual wild species. Recently, differences in the Raman spectra of two wild carrot species have been described in more detail D. carota ssp. gummifer, D. carota ssp. maximus) [17]. Furthermore, Raman mapping clearly presented the different distribution of polyacetylenes in wild and orange carrots. It could be shown that the whole phloem tissue was rich in polyacetylenes, but the maxima were also observed near the pericyclic parenchyma. An analogous distribution of polyacetylenes was found in roots of other carrot wild species. 

A chemical reaction occurs above 1.5 GPa The sample turns black, new peaks develop in the Raman spectrum, and the absorption edge moves below 11,000cm. The recovered material has an optical band gap of 1.39eV, smaller than the band gap of polyacetylene. From the analysis of the Raman spectrum, it is seen that the C=C stretching mode completely disappears in the reaction product, while the C=N stretching band is present but at a different frequency than in cyanocetylene. In addition, the Raman bands of polyacetylene are observed with their characteristic frequency dependence on the wavelength... 

Fig. 3. Raman spectra of ethyne (in polymerized form as a long-chain polyacetylene) on (A) Rh/Al203 and (B) a gold electrode. [(A) Reprinted with permission from Ref. 94. Copyright 1985 American Chemical Society (B) reprinted with permission from Ref. 83. Copyright 1985 American Chemical Society.]...

Transition-metal containing zeolites such as CoY and NiY (but not the Cu, Mn and Zn forms) polymerize acetylene to give trans-polyacetylene with relatively short conjugation length, as indicated by resonance Raman spectroscopy.70 The pol3nmerization products appeared to be restricted to the zeolite crystal surfaces. The authors also point to die importance of Lewis acidic centers for the polymerization. 

Zeolites. The weak Raman signals arising from the aluminosilicate zeolite framework allow for the detection of vibrational bands of adsorbates, especially below 1200 cm which are not readily accessible to infrared absorption techniques. Raman spectroscopy is an extremely effective characterization method when two or more colored species coexist on the surface, since the spectrum of one of the species may be enhanced selectively by a careful choice of the exciting line. A wide range of adsorbate/zeolite systems have been examined by Raman spectroscopy and include SO2, NO2, acety-lene/polyacetylene, dimethylacetylene, benzene, pyridine, pyrazine, cyclopropane, and halogens. Extensive discussions of these absorbate/zeolite studies are found in a review article by Bartlett and Cooney. ... 

MBPT(2) has also been applied to calculate vibrational frequencies of polymers. With the translational symmetry, one can only calculate the vibrational modes with the reciprocal vector k = 0. These modes are of particular importance since they give rise to infrared and Raman spectra [67]. We applied MBPT(2) to polymethineimine and calculated its equilibrium structure, band gap, and vibrational frequencies with basis sets STO-3G, 6-31G and 6-31G [68]. Both basis set and electron correlation have a strong influence on its vibrational frequencies as well as its optimized geometry and band gap. With respect to in-phase (k=0) nuclear displacements, Hirata and Iwata very recently calculated the MBPT(2) vibrational frequencies of polyacetylene for basis sets STO-3G and 6-31G with analytical gradients [69], They showed that MBPT(2) greatly improves the HF vibrational frequencies for polyacetylene. 

P. Tsai, R.P. Cooney, J. Heaviside, and P. Hendra, Resonance Raman Spectra of Polyacetylene on Zeolite and Alumina Surfaces. Chem. Phys. Lett., 1978, 59, 510-513. 

Fink, J. Leisling, G. Momentum-dependent dielectric function of oriented trarw-polyacetylene. Phys. Rev. B 1986, 34(8), 5320-5328 Miyano, K. Maeda, T. Photoluminescence, absorption and Raman spectra of a polydiacetylene. Phys. Rev. B, 1986, 33(6), 4386 388. 

The infrared and Raman spectra of polyacetylene undergo very large changes when the polymer is doped. This is because the electronic structure of the polymer has changed dramatically and infrared and Raman spectral intensities depend on the electronic properties. The metallic nature of the resulting materials also makes measuring the spectra difficult. All of these effects are irrelevant to the neutron so it... 

Fifty-nine references on the application of Raman spectroscopy to polymers are cited in a recent popular book on applications of Raman (139). Polyacetylene and related polymers are being widely investigated at this time (140-143). 

The vibrational contribution to the second hyperpolarizability of polyacetylene is mainly supported by the Raman intensity-related term. Its importance varies according to the optical process 0.5% for EFISHG, 45% for EOKE, 87% for DFWM and 129% for the static second hyperpolarizability. 

---