Isotope effects in the raman spectra of BEDT-TTF and ß-(BEDT-TTF)2I3
Résumé
We have performed a Raman spectroscopic investigation on 13C enriched BEDT-TTF molecules which has been motivated by isotope shift experiments of the superconducting transition in the ßH phase of (BEDT-TTF)2I3 (Tc ≈ 8.2K at mid transition) stabilized at low temperature via the adequate cooling procedure. In the C=C stretching region, two main bands are observed at 1521 and 1468 cm-1, shifted downward compared to the 1555 and 1495 cm-1 in 12C BEDT-TTF, and simple calculations predict very well this shift. Also, these bands are recorded with different intensities. In the Raman spectrum, the 1512 cm-1 mode, assigned to a combination mode, presumbly appears much weaker at 1485 cm-1.