An X-ray Diffraction Study of the Structure of Argon in the Dense Liquid Region

[摘要] X-ray diffraction measurements were made on argon at sixstates in the general liquid region below the critical pressure atdensities between 0.910 to 1.261 gm/cc and at temperatures between108 to 143 °K. The intensity patterns exhibited three distinctmaxima at s values of 1.91 ± .02, 3.68 ± .06 and 5.43 ± .16 Å ^-1.The intensity patterns were Fourier transformed to the net radialdistribution function and the direct correlation function. Thefunctions, 4πr²ρh(r), showed 3 maxima at low densities and 4 at thehigh densities at values of r of 3.85 ± 0.05, 7.29 ± .10, 10.75 ± .45and 14.1 ± .5 Å. A subsidiary maximum between the first and secondmain peaks was observed to increase in prominence and disappearsystematically as the density increased. It was not noticeablyevident at either the lowest or highest density. The first zero ofthe direct correlation function was at an r value of 3.34 ± .03 Å,whereas the first maximum was at 3.78 ± .06 Å. Unlike previousdeterminations of C(r) in this laboratory, the direct correlationfunction exhibited secondary features on the shoulder of the main peak.At the highest density the direct correlation function goes negativenear 6 Å. The intermolecular potential function was calculated fromthe data using the Percus-Yevick equation. At the lowest density thepotential predicted in this way closely resembled the Lennard-Jones12-6 potential for argon. However, the well-depths of these predictedpotentials diminished rapidly with increasing density and decreasingtemperature from 118.0 °K at ρ = .910 to 68.6 °K at ρ = 1.261 gm/cc.Comparisons of the direct correlation function and the radialdistribution function with analytic predictions based on the Lennard-Jonespotential and the P-Y equation indicated internal consistencyat the lower densities. A comparison of the experimental radialdistribution function at the highest density, with one calculatedby molecular dynamics, indicated substantial agreement.

[发布机构] University:California Institute of Technology;Department:Chemistry and Chemical Engineering

[关键词] Chemical Engineering