Thickness of the Surface of Liquid Argon near the Triple Point

Abstract

The coefficient of ellipticity of the liquid-vapor interface of liquid argon has been measured to be $\overline{\rho }\times {10}^4=5.7\mathrm{}\pm 0.4$ at 90°K, rising to 8.8±0.6 at 120°K. Assuming a Fermi density profile and isotropy of the dielectric constant in the interface region, this yields a 10%-90% interface thickness $t\left(90\mathrm{}°\mathrm{K}\right)=7.9\mathrm{}\pm 0.5$ Å and $t\left(120\mathrm{}°\mathrm{K}\right)=15.2\mathrm{}\pm 1.0$ Å, averaged over a surface dimension of the wavelength of light. The measurement is compared with predictions, and theoretical uncertainties are emphasised.