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We report on time-resolved multiphoton ionization and fragmentation dynamics of free Hgnclusters (n ≤ 110) with femtosecond laser pulses. Already at laser intensities of 10 11 W/cm 2 we observe prompt formation of singly, doubly, and triply charged Hgn clusters. In pump-probe experiments short-time (0-5 ps) oscillatory modulations of the transient Hg + n and Hg 2+ n signals are observed which indicate an intermediate state dynamics common to all observed cluster sizes and charge states. Long-time (0-200 ps) transient ionization signals show caged dissociation and recombination chromophore dynamics.PACS. 33.80.Rv Multiphoton ionization and excitation to highly excited states -36.40.Qv Stability and fragmentation of clusters

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We report on studies of multiple ionization and fragmentation of free Hg n (n ≤ 80) clusters in the femtosecond time domain at wavelengths ranging from 255 nm to 800 nm. After excitation by single laser pulses of an intensity of 5 * 10 11 W/cm 2 we observe prompt formation of multiply charged Hg n clusters. The Hg n cluster size distribution observed up to n ≈ 80 shows in additon to singly charged also doubly and triply charged clusters with a surprisingly high amount of doubly charged clusters. The measured cluster size distribution is nearly independent of laser wavelengths. For higher laser intensities (2 * 10 12 W/cm 2 ) we observe multiply charged mercury atoms up to Hg 5+ . At 10 13 W/cm 2 molecules and clusters eventually disappear due to Coulomb explosion and complete Fragmentation. Only atomic ions, singly and multiply charged, with high kinetic energies are then observed.