Time-resolved photo-electron spectroscopy on mass-selected metal clusters using a regenerative femtosecond amplifier up to 100 Hz

A femtosecond photo-electron experiment is described which provides excelle nt conditions for measuring time-resolved photo-electron spectra of free, m onodispersed cluster anions using repetition rates up to 100 Hz. Cluster an ions are synthesized in an electric are and subsequently cooled in a helium carrier gas. A time-of-flight spectrometer is used for mass separation of the negatively charged clusters. The kinetic energy of the photo-electrons is analyzed by a magnetic-bottle time-of-flight spectrometer, which guarant ees a maximum collection efficiency. Femtosecond laser pulses are generated by a seeded regenerative Ti:Sa amplifier, which is externally pumped with the second harmonic of a diode-pumped solid-state Nd:YAG laser. A retrorefl ector mounted on a computer-controlled translation stage serves as a reprod ucible time delay of the probe pulse. The high energy output of the laser p ulses (similar to 3 mJ) in combination with the variable repetition rate an d the high stability of the amplified pulses provide excellent conditions f or recording pump-probe photo-electron spectra of mass-separated cluster an ions even at the fairly low ion density of pulsed plasma cluster sources. F irst results on the electron dynamics of the Pt-3(-) cluster demonstrate th e reliability of the whole system. Further experimental investigations will concentrate on electron-relaxation processes in transition- and noble-meta l clusters as well as on the nuclear and transition-state dynamics of chemi cally reacted adsorbate clusters.