ИСТИНА

Coherent anti-Stokes Raman scattering (CARS) is applied to identify dense phases of carbon dioxide adsorbed in mesoporous glass Vycor with pores of 2 nm in radius. The phases are identified by their Raman shifts corresponding to the CO2 band at 1388 cm-1. The results obtained at low pressures show that the first layer adsorbed on the pore wall and the polymolecular layers adsorbed upon it can be spectroscopically distinguished from each other. Moreover, the spectrum of the polymolecular layers, usually considered as liquid-like, is found to be noticeably shifted from that of the liquid phase, making these two similar phases also distinguishable. After the onset of condensation, the spectrum of appearing liquid phase is found to be at least three-fold broader than that of the bulk liquid. As pressure is increased, it narrows down to the value in the bulk liquid. Observed narrowing is attributed to size enlargement of liquid clusters, which, being initially of few-nanometer-scale in all three dimensions, grow up and merge together with pressure increase, finally turning into a single “infinite” cluster, i.e. bulk liquid. The results demonstrate that the optical spectroscopic diagnostics provides precise characterization of adsorbate phases appearing in mesoporous or even microporous materials without need of any modeling of adsorption or a priori knowledge about the characteristics of pores.