Osnabrück 2002 – wissenschaftliches Programm

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MO: Molekülphysik

MO 11: Femtosekundenspektroskopie IV: molekulare Dynamik

MO 11.1: Vortrag

Mittwoch, 6. März 2002, 16:30–16:45, HS 15/E07

Mass Spectrometry and Molecular Dynamics of Alkali Fluorides — •Cosmin Lupulescu, Andrea Merli, Štefan Vajda, and Ludger Wöste —

The alkali halide clusters (Na_nF_n−1) featuring strong metal bonds and one-excess electron localized either in the halide vacancy or on the alkali atom attached to the ionic subunit are good systems for investigating the ultrafast nuclear dynamics. The natrium-fluoride clusters were prepared in a molecular beam apparatus by adiabatic coexpansion of natrium metal vapor with Ar and SF₆ as carrier gasses. The laser system consists of an Ti:Sa oscillator providing seed pulses for 1 kHz multipass amplifier. The sub-40 fs amplified pulses, centered at 805 nm, are used to pump two travelling-wave optical parametric amplifiers which provide fs pulses in the UV, VIS and IR region. Mass spectra of the alkali halide clusters were measured at different wavelengths in these spectral regions, showing a strong dependence of the individual Na_nF_m(n<7,m<n) peak intensities on the laser wavelength. The study of the dynamics of the excited states is possible by employing pump-probe spectroscopy. First time-resolved spectra will be presented.In the case of Na₂F, the first excited state was reached by an excitation pulse centered at 1200 nm, while the ionization pulse was tuned at 415 nm. The stability of excited state and its sub-ps dynamics will be discussed. The resolved oscillations of the wavepacket are in good agreement with the theoretical calculations.