Berlin 2018 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 68: Surface dynamics: Reactions, elementary processes and phase transitions I

O 68.4: Vortrag

Mittwoch, 14. März 2018, 15:45–16:00, MA 043

Femtosecond laser-induced associative desorption of molecular hydrogen from graphite — •Lorenzo Maddii Fabiani, Robert Frigge, John Thrower, and Helmut Zacharias — Physikalisches Institut, Westfälische-Wilhelms-Universität Münster, Wilhelm-Klemm-Straße 10, 48149 Münster, Deutschland

The formation of molecular hydrogen via radiation-induced associative desorption from dust particles may play an important role in photon dominated regions of the interstellar medium. In this study we investigate the desorption of molecular hydrogen and deuterium from HOPG following surface excitation with fs-laser pulses at λ = 400 nm. Desorbed neutral species are analyzed by internal state selective two-photon ionization (1+1) REMPI in the XUV region.

The desorbing hydrogen molecules show strongly non-equilibrium state populations. The vibrational ground state is less populated than the first excited one, while measurements for higher vibrational states are on-going. State specific kinetic energy measurements result in a value for v″=1, E_kin = 100 meV, significantly lower than for v″=0, E_kin=170 meV. The rotational populations present a non-thermal distribution that can be fitted by two rotational temperatures for low and high J″. The average rotational energy is determined to E_rot=390 cm⁻¹ for v″=0 and 480 cm⁻¹ for v″=1. A nonlinear fluence dependence of the desorption yield allows two-pulse correlation measurements, which give an insight into the relevant desorption mechanisms. The FWHM of ca. 450 fs suggests an electron induced desorption mechanism.