Berlin 2001 – scientific programme

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CPP: Chemische Physik und Polymerphysik

CPP 7: Dynamics of Molecular Systems

CPP 7.3: Talk

Tuesday, April 3, 2001, 17:25–17:45, 112

Isotope effect in thermal diffusion of mixtures of benzene and cyclohexane — •Christian Debuschewitz and Werner Köhler — Physikalisches Institut, Universität Bayreuth, 95440 Bayreuth

We present results of a systematic investigation of the isotope effect on thermal diffusion in mixtures of cylcohexane and benzene. A transient holographic grating technique has been employed for the measurement of the diffusion coefficient D, thermal diffusion coefficient D_T, and Soret coefficient S_T. The mass effect can clearly be separated from other contributions, and S_T can be expressed as a linear function of both the mass difference Δ M and the concentration c: S_T = a Δ M + (c − c₀) b. a and b are fit parameters. The contribution to S_T stemming from the mass difference has been found independent of composition, whereas the mass-independent part depends linearly on c and changes its sign at c₀. The results will be discussed in the light of recent molecular dynamics simulations.