Dresden 2009 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 63: Semiconductor substrates: Adsorption
O 63.3: Vortrag
Freitag, 27. März 2009, 11:45–12:00, SCH A118
Long-lived excitonic desorption of NO from C60/Cu(111) — Tim Hoger and •Helmut Zacharias — Westfälische Wilhelms-Universität Münster
The desorption of NO molecules from a C60/Cu(111) surface is initiated by a 7 ns UV laser pulse (355 nm). The NO molecules are rotational state selectively detected by a frequency-doubled dye-laser (226 nm) by (1+1) REMPI. In a TOF mass spectrometer the arrival time spectrum shows two channels, one fast direct one and a slow one. This is confirmed by measuring directly the velocity distribution of the desorbing NO. The fast channel refers to a DIET process with a hot rotational distribution and a moderate vibrational excitation with a strong rotational-translational coupling. In the slow channel the velocity distribution does not depend on the particular detection time after initiating the desorption by the 355 nm pump pulse. The recorded velocities are further faster than expected from the detection time. It is thus concluded that the desorption occurs time-delayed with respect to the excitation. The lifetime of this excitation can be estimated to approximately 125 µs, in good agreement with lifetimes of triplet excitons in C60. Triplet excitonic states in C60 are possible energy reservoirs for this desorption.