Linewidths and shifts of carbon dioxide CARS spectra near the critical point

Abstract

AbstractTransformation of the Q‐branch in CARS spectra of the low‐wavenumber Fermi dyad 2ν2/ν1 component was studied in CO2 near the critical point (Tc = 31.03 °C, Pc = 72.8 atm). CARS spectra were collected along several isotherms in the temperature and pressure ranges 25.6–36.1 °C and 48–118 atm, respectively. The dependence of linewidth on pressure has an extremum at temperatures >31 °C with a maximum linewidth ∼50% greater than in liquid CO2. The position of the maximum was shifted from the critical to higher pressure with temperature increase. Interpretation of this inhomogeneous broadening is given in terms of cluster microstructure of the supercritical fluid. Copyright © 2003 John Wiley & Sons, Ltd.