Osnabrück 2002 – wissenschaftliches Programm

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MO: Molekülphysik

MO 2: Femtosekundenspektroskopie I: Ladungstransfer

MO 2.2: Vortrag

Montag, 4. März 2002, 14:15–14:30, HS 15/E07

Experiments on vibrational wavepacket motion during ultrafast heterogeneous electron transfer — •Carsten Zimmermann, Sai Ramakrishna, Rainer Eichberger, Winfried Storck, and Frank Willig — Hahn-Meitner-Institut, Glienicker Str. 100, 14109 Berlin

Photoinduced heterogeneous electron transfer was measured with fs transient absorption in ultra-high vacuum for the perylene chromophore attached via an anchor to a nanocrystal of TiO2 that formed a sponge-type layer with a large surface area. The perylene chromophore offers the advantage that absorption spectra of the ground, first excited singlet and ionized state are well separated. Time constants between 35fs and around 200fs were found with spacer-cum-anchor groups of different length and chemical composition. Long flexible bridge groups allowed for several configurations and thus different distances of the perylene chromophore from the TiO2 surface. They gave rise to different time constants for electron injection. Vibrational wavepackets of low energy modes (mainly 360cm-1 and 420cm-1) were generated in the perylene chromophore applying sub-30fs laser pulses. The wavepacket was generated in the donor state, survived the electron transfer reaction and continued its motion in the product state (ionized molecule) for several hundred femtoseconds. The rise of the product state showed a step-wise increase indicating the modulation of heterogeneous electron transfer with 75fs time constant due to the motion of a vibrational wavepacket (480cm-1) in the donor state.