Dresden 2009 – scientific programme
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 7: Liquids
CPP 7.6: Talk
Monday, March 23, 2009, 19:15–19:30, ZEU 160
Molecular motions in liquid medium-chain n-alkanes — •Tobias Unruh1, Christoph Smuda1, Sebastian Busch1, and Gerd Gemmecker2 — 1Technische Universität München, Forschungsneutronenquelle Heinz Maier-Leibnitz (FRM II), D-85747 Garching — 2Technische Universität München, Bayerisches NMR-Zentrum, Chemie Department
Different diffusive motions in liquid medium-chain n-alkanes could be disentangled by resolution resolved quasielastic time-of-flight neutron spectroscopy (TOF-QENS). It was found that the dominating motion causes a Q2-dependence of the QENS signal for any observation time in the picosecond time range. For the longest times the Q2-dependence describes the long range center-of-mass diffusion of the alkane molecules as confirmed by PFG-NMR measurements. By comparison with molecular dynamics simulations, the identified motions for short times are attributed to displacements of hydrogen atoms reflecting local molecular trajectories. Despite the rod-like shape of the molecules the center-of-mass diffusion was found to be essentially isotropic. A coherent picture of the diffusional process ranging from the fast tumbling of CH2 groups to the slow long range molecular diffusion will be presented.