Rayleigh Linewidth in Xenon Near the Critical Point

The Rayleigh linewidth $\Gamma$ of xenon was measured on the critical isochore between 0.003 and 5.0°C above $T_c$. In the hydrodynamic region ($q\xi <~0.2$) we find $\Gamma =q^2{\chi }_0{\left[\frac{(T-T_c)}{T_c}\right]}^{\gamma -\psi }$ with ${\chi }_0=(6.94\mathrm{}\pm 0.21)\times {10}^{-4\mathrm{}}$ ${\mathrm{cm}}^2$/sec, and $\gamma -\psi =0.751\mathrm{}\pm 0.004$. Our data over the entire region $0.009<~q\xi <~6.7$ agree quite well with the recent Kawasaki extended mode-mode coupling theory. However, the Kadanoff-Swift-Kawasaki result $\gamma -\psi =\nu$ does not appear to be valid.