Hannover 2010 – wissenschaftliches Programm
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MO: Fachverband Molekülphysik
MO 18: Cluster I
MO 18.7: Vortrag
Donnerstag, 11. März 2010, 12:00–12:15, F 102
Ultrafast dynamics of the first electronically excited state of neutral water clusters — •Jan P. Müller, Hongtao Liu, Marcus Beutler, Masood Ghotbi, Frank Noack, Wolfgang Radloff, Nickolai Zhavoronkov, C. P. Schulz, and Ingolf V. Hertel — Max-Born-Institute, Max-Born-Str. 2a, 12489 Berlin
Although water is one of the most familiar substances in our life, the spectroscopic and dynamical properties of the electronically excited states of water clusters are still not well known. A great challenge for experiments is creation ultrashort VUV laser pulses, needed to study the ultrafast dynamics, at sufficient energies for coping with the low densities of typical molecular beams. Recently we succeeded to create 45 fs VUV laser pulses having energies up to 300 nJ at a wavelength of 159 nm (5th harmonic of Ti:Sapphire), formed by four wave difference frequency mixing in a gas cell filled with argon. By this means it was possible to study the time resolved dynamics of (H2O)n and (D2O)n clusters in the range n=2−9 for the first time. The photoinduced dynamics of the à state has been investigated by a pump probe scheme, using one VUV photon for excitation and 2−3 photons of 795 nm to ionize the clusters. Except for n = 1 −2, only protonated clusters H(H2O)n−1+ can be observed in the mass spectrum. For all clusters, decay lifetimes in the range of the 10-30 fs and 50-150 fs respectively have been identified. Aditionally an ultrafast process is visible, agreeing well with time scale of 1.8-2.5 fs measured in the group of Fuß for the water monomer. This three decay times can be attributed to OH dissociation, internal conversion and H-ejection.