Theoretical investigation of the ultrafast NeNePo spectroscopy of Au
4
and Ag
4
Clusters |
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Authors: | M Hartmann R Mitrić B Stanca V Bonačić-Koutecký |
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Institution: | Walther-Nernst-Institut für Physikalische und Theoretische Chemie, Humboldt-Universit?t Berlin, Bunsenstrasse 1, D-10117 Berlin, Germany, DE
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Abstract: | Ultrafast ground state nuclear dynamics of Au4 and Ag4 is theoretically explored in the framework of negative ion - to neutral - to positive ion (NeNePo) pump-probe spectroscopy
based on the ab initio Wigner distribution approach. This involves the preparation of a nonequilibrium neutral ensemble by pump induced photodetachment
of a thermal anionic ground state distribution, gradient corrected DFT classical trajectory simulations “on the fly” on the
neutral ground state, and detection of the relaxation process of the ensemble in the cationic ground state by a time-delayed
probe pulse. In Au4, the initially prepared linear structure is close to a local minimum of the neutral state giving rise to characteristic vibrations
in the signals for probe wavelength near the initial Franck-Condon transition. A timescale of ∼1 ps for the structural relaxation towards the stable rhombic D2h neutral isomer was determined by the increase of the signal for probe wavelength in vicinity of the vertical ionization energy
of the rhombic structure. In contrast, the relaxation dynamics in Ag4 is characterized by normal mode vibrations since both the initially prepared anionic ground state and the neutral ground
state have rhombic minimum geometries. Thus, time-resolved oscillations of pump-probe signals are fingerprints of structural
behaviour which can be used experimentally for the identification of particular isomers in the framework of NeNePo spectroscopy.
Received 22 December 2000 |
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Keywords: | PACS 31 15 Qg Molecular dynamics and other numerical methods – 31 15 Ar Ab initio calculations |
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