Key words: subcritical carbon dioxide, nanopores, adsorption and condensation in pores, shift of critical point, CARS-probe
Coherent anti-stocks Raman scattering spectra measured in the range of Q-branch of ν1 vibrational transition are used to reveal the state of carbon dioxide in nanopores of Vicor glass. The measurements were carried out in a high pressure optical cell at room (20.5 °C) and subcritical (30.5 °C) temperatures and CO2 pressures up to saturation value Psat for each temperature. In addition to the main spectral component assigned to gaseous CO2 molecules, the second, low frequency component appears in the spectra at pressures close to Psat. This second component is determined by the contribution of CO2 molecules inside pores. Spectral deconvolution taking into account the interference of these two bands allows one to estimate spectral features of the
second (low-frequency) component for each temperature. The bandwidth of lowfrequency component decreases with CO2 pressure at 20.5 °C, which is caused by transition of CO2 from adsorbed stated to condensed state in the pore. At subcritical temperature 30.5 °C the spectral width of the second component is independent of pressure and corresponds to the value measured in free volume at supercritical conditions, which is likely due to the low-temperature shift of critical point in nanopores.
doi:10.1134/S1990793109070045