Narrowing of the vibrational spectrum under compression of liquid carbon dioxide

The broadening and shift of the Q bands of the 1388/1285-cm⁻¹ Fermi doublet of carbon dioxide have been measured by means of the spectroscopy of coherent anti-Stokes Raman scattering in a wide density range realized at compression in dense gaseous and liquid states. The spectrum of the low-frequency Q band exhibits an essential narrowing upon the compression of the liquid in the density range of 320–400 amagat from a maximum width of about 2.2 cm⁻¹ to about 1.7 cm⁻¹ determined by elastic dephasing. The observed dependence is connected with the progressive narrowing of the spectral contribution attributed to the collapsed rotational structure.