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Direct Imaging of Laser-driven Ultrafast Molecular Rotation
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Ultrafast relaxation dynamics observed through time-resolved photoelectron angular distributions.

Julien Lecointre1, Gareth M Roberts, Daniel A Horke

  • 1Department of Chemistry, University of Durham, South Road, Durham, DH1 3LE, UK.

The Journal of Physical Chemistry. A
|October 22, 2010
PubMed
Summary

Time-resolved photoelectron imaging reveals internal conversion dynamics in the 7,7,8,8-tetracyanoquinodimethane (TCNQ) radical anion. This study quantifies excited-state lifetimes using photoelectron angular distributions, aiding molecular dynamics understanding.

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Area of Science:

  • Physical Chemistry
  • Molecular Spectroscopy
  • Quantum Dynamics

Background:

  • The 7,7,8,8-tetracyanoquinodimethane (TCNQ) radical anion is a key molecule in organic electronics.
  • Understanding its excited-state dynamics is crucial for designing new materials.
  • Previous studies lacked detailed temporal resolution of internal conversion processes.

Purpose of the Study:

  • To investigate the time-resolved internal conversion dynamics of the TCNQ radical anion.
  • To develop a method for extracting population dynamics from overlapping photoelectron signals.
  • To determine the lifetime of the first excited state of TCNQ radical anion.

Main Methods:

  • Time-resolved photoelectron imaging (TRPI) was employed.
  • Photoelectron angular distributions (PADs) were analyzed using the s-p model.
  • A novel formulism was developed to analyze spectrally overlapping features.
  • The β(2) anisotropy parameter was utilized to extract population dynamics.

Main Results:

  • Temporal changes in PADs indicated internal conversion from the excited state to the ground state.
  • The developed formulism successfully extracted population dynamics from overlapping spectral features.
  • The lifetime of the first excited state was determined to be in good agreement with TRPI data.

Conclusions:

  • Time-resolved photoelectron imaging provides insights into the ultrafast internal conversion of TCNQ radical anion.
  • The developed analysis method is effective for studying complex molecular systems with overlapping spectral features.
  • Accurate excited-state lifetime measurements are essential for understanding photochemical processes.