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MO: Molekülphysik

MO 20: Schwingung und Rotation

MO 20.3: Talk

Friday, March 26, 2004, 11:30–11:45, HS 355

Free Rotation of Paraterpenyl in PMMA Nanocavities — •Christian Spitz, David von Seggern, and Ralf Menzel — Universität Potsdam, Institut für Physik, Am Neuen Palais 10, 14469 Potsdam

By the use of transient grating diffraction measurements the population dynamics as well as the polarization dynamics in thin films can be investigated on a ps timescale. In this technique a pair of pump beams modulates the sample absorption with its interference pattern. Subsequently, a probe beam is diffracted on the population grating as well as on the polarization grating.

In this paper the excited state behaviour of p-terphenyl in cyclohexane solution and in a rigid poly(methyl methacrylate) (PMMA) film is reported. In both cases the signal shows a biexponential decay with a slower component corresponding to the excited state lifetime. The faster time constant is predicted for rotational reorientation in the case of liquid solution. Unexpectedly in the rigid film this reorientation becomes even faster which is discussed in terms of a free volume effect. This would predict the existence of nanocavities in PMMA of much bigger size than observed so far.