Coherent anti-Stokes Raman scattering (CARS) spectroscopy is applied to probe the microstructure of CO2 adsorbed in nanoporous glass Vycor with a mean pore radius of 2 nm. CARS spectra of the Q-branch (1388 cm-1) were measured at 22 °C at pressures decreasing in a range providing the transition from the condensed phase in the whole volume of the pores to submonolayer coverage on their walls. The spectral behavior demonstrates sequential changes in the fluid state inside the nanopores. The analysis of the experimental results allowed us to characterize and compare the spectral properties of gas-like, liquid-like, and surface adsorbed carbon dioxide. The results provide clear evidence that as the surface coverage is decreased, the vibrational frequency shifts down. Copyright © 2014 John Wiley & Sons, Ltd.