The composition dependence of the thermal diffusion factor for3Hesngbnd;4Hemixtures was measured at nine temperatures ranging from 5.5 to 240deg;K in a sevenhyphen;tube trennschaukel. A pronounced dependence upon the heliumhyphen;3 content was observed which increased with decreasing temperature and which was also linear in 1sol;agr;T, in accord with theory. The experimental data were compared with theoretical thermal diffusion factors calculated quantum mechanically using several different helium potentials. Both our experimental and theoretical results indicate a rather weak temperature dependence with agr;Trising slowly with decreasing temperature in the temperature region investigated. This is in sharp constrast to the results of van der Valk, who observed a rapid rise from 40deg;K down to 14deg;K. On the basis of the ``sensitive'' regions of the transport properties to the intermolecular potential, as reported by Hanley and Klein, we prefer either Beck's or the Morsehyphen;VDDpotentials on the basis of the data above 50deg;K. However, we were unable to discriminate among potentials from the 5.5deg;K experiments since the ``insensitive'' region extended to a much lower temperature than anticipated.
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