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Coherent phase control of internal conversion in pyrazine.

Robert J Gordon1, Zhan Hu2, Tamar Seideman3

  • 1Department of Chemistry (m/c 111), University of Illinois at Chicago, Chicago, Illinois 60680-7061, USA.

The Journal of Chemical Physics
|April 17, 2015
PubMed
Summary

Ultrafast laser pulses controlled pyrazine ionization dynamics. A genetic algorithm optimized pulse shaping, revealing distinct control mechanisms for early and late time targets, differing from classical predictions.

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Area of Science:

  • Physical Chemistry
  • Quantum Dynamics
  • Laser Spectroscopy

Background:

  • Pyrazine ionization dynamics are complex, influenced by electronic states and internal conversion processes.
  • Understanding ultrafast molecular dynamics requires advanced spectroscopic techniques.

Purpose of the Study:

  • To investigate the control of electronically excited pyrazine ionization using shaped ultrafast laser pulses.
  • To differentiate between classical and non-classical ionization behaviors under laser control.

Main Methods:

  • Pump-probe spectroscopy utilizing shaped ultrafast laser pulses.
  • Application of a genetic algorithm (GA) with phase-only modulation for pulse optimization.
  • Analysis of ion growth curves as a function of pump/probe delay.

Main Results:

  • Classical rate equations accurately described ionization without pulse shaping.
  • GA-optimized pulses exhibited non-classical ionization dynamics, with distinct behaviors for target times T < 1.5 ps and T > 1.5 ps.
  • Two control mechanisms were identified: wave packet localization for early times and reduced absorption/incoherent decay for late times.

Conclusions:

  • Shaped ultrafast lasers offer precise control over molecular ionization pathways.
  • The observed non-classical dynamics provide insights into wave packet behavior on potential energy surfaces.
  • GA-based pulse shaping is a powerful tool for manipulating quantum dynamics.