Diagnostics of the Critical State of Carbon Dioxide

For the first time, the temperature dependence of the density variance and the correlation length of critical density fluctuations is determined from the experimental data on small-angle light scattering by a CO2 medium. It is found that, at the critical density of CO2 in the temperature range of 10(-8)T(c) < |T - T-c| < 10(-4)T(c) (where T-c is the critical temperature), the correlation length of density fluctuations decreases by 20% as the critical point is approached. The value of density variance does not demonstrate a power-law-type divergence: it remains almost constant within regions of T >= T-c and T <= T-c, but undergoes a 25% jump when passing through the critical point, which may be due to the peculiarities of the experimental set up.