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Journal Article

Infrared multiphoton ionization of superhot C60 : Experiment and model calculations.


Helden,  Gert von
Molecular Physics, Fritz Haber Institute, Max Planck Society;


Sartakov,  Boris
Molecular Physics, Fritz Haber Institute, Max Planck Society;


Meijer,  Gerard
Molecular Physics, Fritz Haber Institute, Max Planck Society;

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Bekkerman, A., Kolodney, E., Helden, G. v., Sartakov, B., Heijnsbergen, D. v., & Meijer, G. (2006). Infrared multiphoton ionization of superhot C60: Experiment and model calculations. The Journal of Chemical Physics, 124, 184312-1-184312-11. doi:10.1063/1.2193520.

Cite as: https://hdl.handle.net/11858/00-001M-0000-0011-048E-9
We address, both experimentally and theoretically, the issue of infrared (IR) resonance enhanced multiphoton ionization (IR-REMPI) and thermally induced redshifts of IR absorption lines in a very large and highly vibrationally excited molecular system. Isolated superhot C60 molecules with well defined and variable average vibrational energy in the range of 9–19 eV, effusing out of a constant flux thermal source, are excited and ionized after the absorption of multiple (500–800) infrared photons in the 450–1800 cm–1 spectral energy range. Recording the mass-selected ion signal as a function of IR wavelength gives well resolved IR-REMPI spectra, with zero off-resonance background signal. An enhancement of the ion signal of about a factor of 10 is observed when the temperature is increased from 1200 to 1800 K under otherwise identical conditions. A pronounced temperature dependent redshift of some of the IR absorption lines is observed. The observations are found to be in good agreement with a model which is based on the sequential absorption of single photons, always followed by instantaneous vibrational energy redistribution. The mass spectra (C⁺60 fragmentation pattern) are found to be strongly excitation wavelength dependent. Extensive fragmentation down to C⁺32 is observed following the absorption of 1350–1400 cm–1 as well as 1500–1530 cm–1 photons while negligible fragmentation is observed when exciting around 520 cm–1.