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MO: Fachverband Molekülphysik

MO 7: Poster: Femtosecond Spectroscopy

MO 7.19: Poster

Dienstag, 9. März 2010, 16:00–18:30, Lichthof

Rotational decoherence in nitrogen investigated by non-adiabatic alignment — •Anna Ott, Nina Owschimikow, Falk Königsmann, and Nikolaus Schwentner — Institut für Experimentalphysik, Freie Universität Berlin

The superposition of rotational states in a wave packet upon excitation of a molecule with anisotropic polarizability with a short, intense laser pulse leads to the appearance of periodic revivals of alignment. We detect alignment in nitrogen gas by the ultrafast Kerr effect method and observe the decay of the coherent signal induced by collisions in pure nitrogen and in gas mixtures of nitrogen with hydrogen and argon. From the decay rates we extract cross sections for decoherence, containing the sum of the effects of energy transfer and pure dephasing. The cross sections decrease with increasing temperature, leading to long lived coherence at high temperatures. Quantitative comparison with depopulation cross sections from measurements of linewidth broadening of the Raman Q-Branch in the literature shows that decoherence in rotational alignment decays at the same rate as the excited population. Thus, in the investigated system there occurs no pure rotational dephasing and all decoherence events are connected with the transfer of energy.