Dissipation and Coherence: Halogens in Rare Gas Solids

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Dissipation and CoherenceHalogens in Rare Gas
Solids
M. Bargheer, M. Gühr, P. Dietrich, M. Fushitani,
T. Kiljunen and N. Schwentner
Institut für Experimentalphysik

• 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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Diatomics in Solid Rare Gas

• I2 in Kr
• Fcc lattice, closest packing
• Adiabatic dynamics including dissipation are
  well described in classical simulations

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Energy loss from oscillations
Bargheer et al., PCCP 4, 75 (2002)
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Energy loss from signal envelope
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Vibrational relaxation ofI2/Kr
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Vibrational relaxation ofI2/Kr, ClF/Ar and Cl2/Ar
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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!

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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
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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

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Dispersion in Morse-Potential (Classical)

• Morse-potential
• Frequency

R
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Dispersion of I2-Wave-Packets
If N number of excited vibrational levels
Tdisp 2 ps Tdisp 5 ps
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Dispersion of ClF-Wave-Packets
Tdisplt 1 ps
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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)
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Explanation in Frequency Domain

• Pulse-Pairs in frequency domain yield spectral
  interferences, if pulses overlap.
• Frequency resolution of monochromator broadens
  pulses.

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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 gt oscillation
  of free molecule?

Cl2 / Ar
constructivedestructive no interference
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Summary

• Signatures of relaxation
• Energy loss of halogens in Rg
• Collisions cause coherence
• Dispersion in anharmonic potentials
• Experiments with phase-locked pulse pairs