Darmstadt 2008 – wissenschaftliches Programm

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MO: Fachverband Molekülphysik

MO 4: Femtosekundenspektroskopie II

MO 4.9: Vortrag

Montag, 10. März 2008, 18:30–18:45, 3G

Rotational diffusion measured by optical transient anisotropy — •Oliver Schalk and Andreas-Neil Unterreiner — Universität Karlsruhe (TH), Lehrstuhl für Molekulare Physikalische Chemie, 76128 Karlsruhe

Rotational diffusion in real time can be observed by transient anisotropy, which is often interpreted in terms of correlation functions. However, anisotropy is sensitive to the transition dipole moment (i.e., only 2 dimensions are to be considered) which leads to a modified decay mechanism. To consider anisotropy explicitly, a new ansatz is shown where rotational diffusion is described by a step model that is able to interpolate between free rotation and media with high viscosities. For collision-free reorientation, a different initial decay and long-time behavior is obtained and compared to models based on correlation functions − however, the new ansatz describes the experiments more satisfactorily. The behavior of collisional anisotropy decay has been modeled by means of Monte-Carlo simulations allowing for a variation of angular correlation and energy transfer. As shown, this approach is easily extendable to multiphoton processes.