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Li, H.; Mignolet, B.; Wang, Z.; Betsch, K. J.; Carnes, K. D.; Ben-Itzhakt, I.; Cocke, C. L.; Remacle, F.; Kling, M. F. (2016): Transition from SAMO to Rydberg State Ionization in C-60 in Femtosecond Laser Fields. In: Journal of Physical Chemistry Letters, Vol. 7, No. 22: pp. 4677-4682
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Abstract

The transition between two distinct ionization mechanisms in femtosecond laser fields at 785 nm is observed for C-60 molecules. The transition occurs in the investigated intensity range from 3 to 20 TW/cm(2) and is visualized in electron kinetic energy spectra below the one-photon energy (1.5 eV) obtained via velocity map imaging. Assignment of several observed broad spectral peaks to ionization from superatom molecular orbitals (SAMOs) and Rydberg states is based on time-dependent density functional theory simulations. We find that ionization from SAMOs dominates the spectra for intensities below 5 TW/cm(2). As the intensity increases, Rydberg state ionization exceeds the prominence of SAMOs. Using short laser pulses (20 fs) allowed uncovering of distinct six-lobe photoelectron angular distributions with kinetic energies just above the threshold (below 0.2 eV), which we interpret as over-the-barrier ionization of shallow f-Rydberg states in C-60.