Vibrational echo studies of pure dephasing: Mechanisms in liquids and glasses

Temperature dependent vibrational dephasing experiments are presented on the asymmetric CO stretching mode (2010 cm(-1)) of (acetylacetonato)bicarbonylrhodium(I) in the solvent dibutylphthalate in both the glass and liquid. The pure dephasing temperature dependence is linear (T-1) at very low temperature and an activated process (Delta E = 385 +/- 50 cm(-1)) above approximate to 20 K. Pure dephasing mechanisms are proposed. It is suggest that the T-1 dependence arises from dynamics of the glass' two level systems, while the activated process involves coupling of the CO stretch to a low frequency intramolecular mode. The experimental results are contrasted with vibrational dephasing experiments on W(CO)(6) also in dibutylphthalate.