Hamburg 2009 – scientific programme
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MO: Fachverband Molekülphysik
MO 19: Spektroskopie in He-Tröpfchen
MO 19.2: Talk
Thursday, March 5, 2009, 14:30–14:45, VMP 6 HS-F
Cold cluster reactions inside helium nanodroplets — •Severin Müller1, Sebastian Krapf2, Thorsten Koslowski2, Marcel Mudrich1, and Frank Stienkemeier1 — 1Physikalisches Institut, Universität Freiburg, 79104 Freiburg, Germany — 2Institut für Physikalische Chemie, Universität Freiburg, 79104 Freiburg, Germany
Helium nanodroplets offer the possibility to investigate complexes of atomic and molecular constituents at a temperature of 380 mK. This low-energy environment is especially interesting for the study of reactive species, since even low energy barriers will greatly affect the dynamics of chemical reactions. We have studied the reaction of alkali clusters AkN (Ak=Na, K, Rb, Cs) with water clusters H2OM embedded in helium nanodroplets by mass spectrometry. After picking up water molecules and alkali atoms, respectively, the droplets were ionized by the output of a Ti:Sa fs laser or by the impact of electrons crossing the droplet beam.
Our results clearly show large differences in the reactivity for the different alkali species. While sodium clusters NaN form large van der Waals-bound complexes with water, cesium clusters CsN undergo chemical reactions to form hydroxide clusters. Upon ionization, these clusters fragment along competing decay channels. The experimental data are backed up by high-level quantum chemical calculations. The abundance patterns found in the mass spectra are explained by the stabilities of different cluster ions with regard to fragmentation and are largely independent of the applied ionization scheme.