Dresden 2006 – scientific programme
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O: Oberflächenphysik
O 17: Adsorption II
O 17.7: Talk
Tuesday, March 28, 2006, 12:45–13:00, TRE Phys
Velocity distributions of NO desorbed from C60/Cu(111) by UV laser excitation — •Daniel Grimmer, Tim Hoger, and Helmut Zacharias — Westfälische-Wilhelms Universität, Physikalisches Institut, Wilhelm-Klemm-Str. 10, 48149 Münster
NO laser desorption experiments have been performed using C60 grown on a poly-Cu cristal. A bimodal distribution of the kinetic energy results in a fast and a slow channel. The fast channel peaks at a velocity of v=1000 m/s for low rotational states and increases to 1300 m/s for high rotational states. The slow channel’s velocity can be fitted by a Maxwellian flux distribution of Tkin=110 K showing deviations at slow velocities (Surf. Sci., submitted).
For C60 epitaxially grown on Cu(111) similar results with respect to the kinetic energies and rotational population are obtained. A slightly higher vibrational population is detected.
In these experiments the velocity was inferred from the arrival time in a pump-probe arrangement. The transformation of the delay into a velocity distribution then yields very slow molecules, too slow to be explained by thermal desorption since the kinetic temperature is clearly much below the surface temperature. Diffusion processes or long-lived excited states could cause such a delayed desorption.
Here we present new velocity distributions of NO desorbed from C60/Cu(111) directly measured by a field-free flight time tube.
This work has been supported by the Deutsche Forschungsgemeinschaft via the Schwerpunktprogramm SPP1093 under project number Za110/21.