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The ultrafast electron relaxation dynamics of anionic and neutral Au25(SR)18 nanoclusters are investigated using broad-band time-resolved optical spectroscopy. From an analysis of the wavelength-dependent transient absorption kinetics, we have obtained valuable information on the spectral features that originate from excitation of “core” and “core−shell” states. In both clusters, photoexcitation occurs into two nondegenerate states near the HOMO−LUMO gap that are derived from the core orbitals. A large difference in the lifetime of the core excitations is observed, with Au25(SR)18− exhibiting a decay rate more than 1000 times slower than the neutral cluster. Both clusters show strong coupling to two different coherent phonon modes, which are observed at 2.4 and 1.2 THz. The electron−phonon coupling is analyzed in terms of the spectral distribution and damping of the coherent modes.
Qian et al. (Thu,) studied this question.