11 research outputs found
Evidence for coupling between collective state and phonons in two-dimensional charge-density-wave systems
We report on a Raman scattering investigation of the charge-density-wave
(CDW), quasi two-dimensional rare-earth tri-tellurides Te (= La, Ce,
Pr, Nd, Sm, Gd and Dy) at ambient pressure, and of LaTe and CeTe under
externally applied pressure. The observed phonon peaks can be ascribed to the
Raman active modes for both the undistorted as well as the distorted lattice in
the CDW state by means of a first principles calculation. The latter also
predicts the Kohn anomaly in the phonon dispersion, driving the CDW transition.
The integrated intensity of the two most prominent modes scales as a
characteristic power of the CDW-gap amplitude upon compressing the lattice,
which provides clear evidence for the tight coupling between the CDW condensate
and the vibrational modes
TORSIONS AROUND THE THE SINGLE BOND IN CONJUGATED MOLECULES
Author Institution: Mellon InstituteThis paper deals with torsions around the single bond in molecules containing the group . Butadiene and glyoxal (OCH-CHO) are prototypes. Benzaldehyde is included as an example of the system [FIGURE]-C=. Torsional frequencies have been observed between 40 and for a dozen such compounds in the vapor state. The evaluation of a potential function from the infrared frequency is difficult, if not impossible. If it is written as the usual series [FIGURE] at least two of the three parameters , and are important for the butadiene and glyoxal derivatives. Since there is only one experimental datum, the dilemma is obvious. Nevertheless some interesting comparisons can be made between compounds. For benzaldehyde, and are zero by symmetry and can be evaluated. The barrier for benzaldehyde is very different in the gas and the liquid states