Osnabrück 2002 – scientific programme
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MO: Molekülphysik
MO 19: Poster II (Energietransfer, Reaktionen, Photoionisation, Femtosekundenspektroskopie, ultrakurze Pulse)
MO 19.10: Poster
Thursday, March 7, 2002, 17:30–19:30, Schloss
Quantum effects in a molecular oscillator strongly coupled to a bath: I2 in Kr solids — •Markus Gühr1, Matias Bargheer1, Peter Dietrich2, and Nikolaus Schwentner1 — 1Experimentalphysik FU-Berlin, Arnimallee 14, 14195 Berlin — 2803-1000 Castle Hill Cres., Ottawa ON, K2C 3L7, Canada
The I2 molecule isolated in Kr solids is a realization of an anharmonic oscillator strongly coupled to a bath of Kr atoms. We derive the vibration frequency ω e, anharmonicity ω exe and energy dissipation dE/dt by femtosecond pump-probe spectroscopy of wave packet dynamics. The strong coupling leads to energy losses of up to 30 vibrational quanta in one collision. Nevertheless vibrational coherences survive for 20 periods. Wave packets can be focused after several oscillations by chirped pulse excitation and even rephasing of an initially prepared wavepacket is observed after 10 ps. Conventionally, strong system-bath coupling is thought of as a severe source of decoherence. However, ultrafast collisions can prepare vibrationally coherent wavepackets that are not excited directly with a laser pulse, if the geometry and timing of the inelastic scattering events are well defined.
Trajectory calculations were successfully applied to simulate the early wave packet dynamics. After several periods a new oscillational pattern with approximately half vibrational frequency and an interesting dependence on the probe window is observed in the spectra. We analyze the data with respect to interference effects beyond the classical limit.