RAMAN BAND-SHAPE ANALYSIS OF OXOCARBON IONS IN AQUEOUS-SOLUTIONS

Fourier analysis of Raman bandshapes was undertaken for some modes of the lithium salts of squarate (C4O42-) and croconate (C5O52-) ions in saturated aqueous solution. Time correlation functions obtained from t he isotropic and anisotropic Raman components of the totally symmetric modes of ring breathing, and the ones obtained from the anisotropic c omponents of the non-totally symmetric modes of C-C stretching and rin g bending, have similar decay rates for both C4O42- and C5O52-, indica ting that reorientation is very hindered in these systems for both spi nning and tumbling of the main symmetry axis. The experimental vibrati onal correlation functions were fitted by the Kubo's equation, and are in the intermediate modulation regime, although faster than the ones for other typical ions reported in literature, The small time correlat ion of vibrational frequency fluctuations (approximate to 0.1 ps) toge ther with slow reorientation imply the picture of the ions performing librational motions inside temporary cages formed by water molecules, From the modeling of the vibrational and reorientational correlation f unctions, the estimated average librational frequency is ca, 80 cm(-1) . Known models which separate homogeneous and inhomogeneous contributi ons give no better fitting of the vibrational correlation functions, T he homogeneous nature of the vibrational dephasing process is also poi nted by the almost perfect Lorentzian shape of the bands and by the ca lculation of the isotropic components by a memory function approach tr uncated in second order, Similar results were found after a 1.10 dilut ion of the saturated solutions, or upon increasing the temperature to 50 degrees C, or yet by using of the sodium salts.