Berlin 2012 – scientific programme

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O: Fachverband Oberflächenphysik

O 12: Surface dynamics

O 12.3: Talk

Monday, March 26, 2012, 16:30–16:45, H 2013

Time-resolved laser-induced desorption of atomic Deuterium and Hydrogen from HOPG — •Robert Frigge and Helmut Zacharias — Physikalisches Institut, Universität Münster, Germany

Formation processes of molecular hydrogen upon radiation of adsorbed atoms on graphitic dust particles play an important role in the interstellar circuit of matter. However, the conversion process is still not fully understood yet.
Atomic hydrogen desorption from HOPG is examined after surface excitation with fs-laser pulses at λ = 400 nm. Desorbed neutral H atoms are ionized using (2+1) REMPI via the 2s ← 1s transition, and are detected with a time-of-flight mass spectrometer. Velocity distribution measurements result in three maxima for fast, medium and very slow desorbed hydrogen atoms. By electron scattering calculations [1] of the vibrational excitation of the H-C bond the three maxima can be addressed with different adsorption potentials, depending upon the neighboring H atom position on the graphene lattice [2,3]. A nonlinear fluence dependence of the desorption yield allows two pulse-correlation experiments. As a result we derive a pulse-delay dependent yield with a FWHM of about 700 fs with a coverage dependent variation. This correlation time indicates short lifetimes of the excited electrons and supports a calculation in the DIMET model.
 [1]R. Frigge et al., Phy. Rev. Lett., 104, 256102 (2010)
 [2]L. Jeloaica, V. Sidis, Chem. Phys. Lett., 300 157 - 162 (1999)
 [3]L. Hornekær et al., Phy. Rev. Lett., 97, 186102 (2006)