Force constants for unlike molecules on Exp-six model from thermal diffusion

Abstract

The potential parameters for the unlike pairs of molecules Ne-A, Ne-Kr and A-N 2 have been determined for the Exp-six model from the temperature dependence of thermal diffusion of these gas mixtures following the method developed earlier by Srivastava and Madan. The method of translations given by Mason and Rice was employed to determine the parameters α 12 and ɛ 12 by successive approximations, taking into account also the small temperature variation of the ‘ g ’ factor and utilising Kihara's first approximation formula. The parameter ( ν m ) 12 was found by substituting the appropriate values of α 12 and ɛ 12 in the theoretical expressions for binary viscosity, inter-diffusion or thermal diffusion and utilising the experimental data. The values of the unlike parameters α 12 , ɛ 12 and ( ν m ) 12 thus obtained were utilised to calculate the thermal diffusion factor at different temperatures, using Kihara's expression, and the results obtained were found to agree with the experimental data within the limits of experimental error, thereby confirming the values of the potential parameters. The results show that ( ν m ) 12 could be calculated from the absolute value of the thermal diffusion factor if Kihara's first approximation formula is utilised and correct values of α 12 and ɛ 12 substituted. The combination rules for unlike potential parameters given by Mason and Rice have been found to be inadequate and simpler combination rules have been suggested.