ИСТИНА

Coherent anti-Stokes Raman spectroscopy (CARS) is applied to study dense phases composition in a wide pressure range of carbon dioxide adsorbed in nanoporous glasses with pores of several nm in radius. The phases are recognized by their Raman shifts corresponding to the carbon dioxide vibrational band at 1388 1/cm. The following stages of adsorption are observed spectroscopically: monolayer formation, appearance of liquid-like domains, capillary condensation. Each of the phases is identified by its specific Raman shift. The relative mass fractions are estimated by the analysis of the spectral contributions of the phases. The results show that the liquid-like phase appears in the pores at pressure that is several times smaller than the capillary condensation pressure, at that the pore wall coverage is of the order or even less than a monolayer. The appearance of the liquid-like phase may be attributed to the layers adsorbed beyond the monolayer or to small liquid-like clusters arising in some specific areas of the porous network, which are characterized by strong confinement accompanied with high surface curvature. The density of the liquid-like layers (or clusters), estimated by the spectral shift, appears to be similar to that in the bulk liquid. The results demonstrate that the nonlinear optical spectroscopic diagnostics provides detailed recognizing of adsorbate phases appearing in transparent nanoporous materials.