The frequency dependence of 26 Raman active phonons in TCNQ crystals has been investigated as a function of temperature. Although all phonon frequencies decrease upon increasing the temperature, those at 152 and 160 cm−1 do the opposite. In general, the phonons in the middle frequency region are less sensitive to temperature than those at low and high frequency. We attribute this to mixing of the internal and external modes. By combining the pressure data with the temperature data, we have estimated the intrinsic and extrinsic contribution to the frequency changes. Volume dilatation effects are dominant for frequencies up to 400 cm−1, but phonon–phonon interactions are also present. The half-width of the phonons was measured, both at room temperature and liquid nitrogen temperature. It goes through a maximum for the phonons in the 300 cm−1 region and a minimum for those in the 1000 cm−1 region. The CN groups appear to be loosely attached to the quinone ring.

No abstract

No abstract

The reflectivity spectrum from the (001) surface of TCNQ crystals was recorded between 4200 and 50 cm−1. Only two peaks were observed. The ωLO, ωTO, γLO, and γTO for each mode are 226, 224, 11.4, 6.9, and 477, 476, 5.2, and 3.4 cm−1 respectively; εx is 2.49 for each mode. These data show weak dipole moments in the compound. The absorption spectrum in the same region was also recorded. Three hundred and twenty-seven transitions were observed, most of which were overtones and combinations. The temperature dependence (10–300 K) of the phonons was obtained. Its behaviour confirms mode mixing in the crystal. The reflectivity spectrum and the soft modes occur approximately in the region where one expects a gap between the internal and external modes. We associate charge transfer with mode mixing.

Ethyl-, propyl-, and benzyl-guanidine nitrates were prepared from amine nitrates and calcium cyanamide or dicyandiamide. C a r b o~~a l k~l g~~a n i d i n e s were made by condensing the corresponding amino acids with guanidine carbonate in aqueous medium. All the guanidine nitrates, except the benzyl derivative, were converted into the corresponding nitrogl~anidines by treatment with concentrated sulphuric acid. Esters and metal salts of 1-(a-carbosyalkyl)-2-nitroguanidines were also prepared.

Die tautomeren Formen (I), (II) und (III) einiger 3‐Carbäthoxy‐5‐pyrazolinone werden anhand von NMR‐, IR‐ und UV‐Spektren [Tabellen (NMR, IR) und Abbildungen (UV)] diskutiert.

Using the argon ion laser, the krypton ion laser, and the helium-neon laser, we have measured the Raman intensity of 13 phonons of TCNQ crystals, both at room temperature and at liquid nitrogen temperature. Besides the well-known resonance in the blue region (22 200 cm-'), we have also observed weaker resonances at 19 000 and 15 000 (f2000 cm-I). The shape of the resonances is phonon dependent; the temperature behaviour is also phonon dependent. The results were reproducible on samples grown in three different laboratories. In only one sample did we also observe a fluorescence spectrum which is similar to the resonance Raman spectrum. From X-ray studies of the samples used. we deduce that there are slight structural differences among the samples, but the resonance Raman effect is independent of these differenccs. We surmise that the Raman intensity is sensitive to the presence of the TCNQT radical anion in the crystals. The anion is formed either by impurities or by the photon.En utilisant le laser ionique a I'argon, le laser ionique au krypton et le laser helium-nCon, nous avons mesurt I'intensitt Raman de 13 phonons de cristaux de TCNQ. a temperature ambiante et a la temptrature de I'azote liquide. En plus de la rtsonance dCjh bien connue dans le bleu (22 200 cm-I), nous avons aussi observt des rtsonances plus faibles i 19 000 et 15 000 ( f 2000) cm-'. La forme de ces resonances dtpend des phonons, de meme quc leur comportement en fonction de la temptrature. Les rtsultats Ctaient reproductibles pour des cristaux fabriquts dans trois laboratoires diffkrents. Dans un seul Cchantillon, nous avons aussi observC un spectre de fluorescence qui est semblable au spectre Raman de rtsonance. De 1'Ctude aux rayons X des Cchantillons utilisCs, nous dCduisons qu'il y a de Itgkres diffirences de structures entre ces Cchantillons, mais I'effet Raman de rdsonance est inddpendant de ces difftrences. Nous conjecturons que I'intensitC Raman est sensible i la presence du radical TCNQ' a I'ttat d'anion dans le cristal. L'anion est form6 soit par des impuretts, soit par le photon.[Traduit par le journal]Can.

No abstract