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Dissipation and Coherence: Halogens in Rare Gas Solids. Signatures of Dissipation in Pump-Probe Spectra Dissipation of Energy in Excited Halogens Dispersion and „Decoherence“: Classical vs. Quantum Effects New Experiments with Phase-Locked Pulses.
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Dissipation and Coherence:Halogens in Rare Gas Solids • Signatures of Dissipation in Pump-Probe Spectra • Dissipation of Energy in Excited Halogens • Dispersion and „Decoherence“: Classical vs. Quantum Effects • New Experiments with Phase-Locked Pulses M. Bargheer, M. Gühr, P. Dietrich, M. Fushitani, T. Kiljunen and N. Schwentner Institut für Experimentalphysik
strong coupling to „solvent“ • some similarities to gas phase Diatomics in Solid Rare Gas • I2 in Kr • Fcc lattice, closest packing • Adiabatic dynamics including dissipation are well described in classical simulations
Energy loss from oscillations Bargheer et al., PCCP 4, 75 (2002)
well defined timining of collision • well defined scattering geometry! Collisions Cause Coherence? Collision of I2 with surrounding Kr • Width of wavepacket: 500 cm-1 • Energy loss in collision: 1500 cm -1 • Collision populates new vibrational levels coherently!
DE Mechanisms of „Dephasing“ • Decoherence due to collisions with solvent (pure dephasing T2´) • Population decay by vibrational relaxation (and non-adiabatic couplings) (relaxation time T1) • Dispersion due to anharmonicity (dispersion time Tdisp) Energy R
Dispersion: Classical and Quantum Effects • Compensation of dispersion by negative chirp of excitation pulse • Classical! • Rephasing of wavepacket after dispersion • Rephasing time Trep = 1/wexe (after dispersion of the packet) • discrete vibrational levels needed
Dispersion-time:(wave packet width DT > 1/2Tmorse) T1 DT = n(T1 - T2) Energy DE T2 Dispersion in Morse-Potential (Classical) • Morse-potential: • Frequency: R
Dispersion of I2-Wave-Packets If N = number of excited vibrational levels: Tdisp= 2 ps Tdisp= 5 ps
Dispersion of ClF-Wave-Packets Tdisp< 1 ps
Experiments with Phase-Locked Pulses Constructive Interference Destructive Interference Generation of Pulse-Pairs: Piezo Piezo tunes phase by moving distance l/2 Scherer et al., J. Chem. Phys. 95, 1487 (1991)
Observed signal: Fluorescence, i.e. integrate from -∞ to +∞ • Vibrational states act as a monochromator => interference constructivedestructive no interference Explanation in Frequency Domain • Pulse-Pairs in frequency domain yield spectral interferences, if pulses overlap. • Frequency resolution of monochromator broadens pulses.
Excitation of phonon sidebands => dissipative dynamics • Coherent control of dissipative vs. free wave packet motion Phase-Locked Pulses in the Presence of Dissipation: Proposed Experiment: Cl2 in Ar • Phonon side-bands increase for higher vibrational levels • Excitation of zero-phonon lines => oscillation of free molecule? Cl2 / Ar constructivedestructive no interference
1.0 10 states 0.8 4 states simulated signal 0.6 0.4 0.2 0.0 0 1 2 3 4 5 t / ps Summary • Signatures of relaxation • Energy loss of halogens in Rg • Collisions cause coherence • Dispersion in anharmonic potentials • Experiments with phase-locked pulse pairs