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Post-shock relaxation in crystalline nitromethane.

Luis A Rivera-Rivera1, Thomas D Sewell, Donald L Thompson

  • 1Department of Chemistry, University of Missouri-Columbia, Columbia, Missouri 65211-7600, USA.

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|March 8, 2013
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Summary

Molecular dynamics simulations reveal shock wave relaxation in crystalline nitromethane. Thermal equilibrium is reached in picoseconds, with altered bond strengths indicating significant shock compression effects.

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Area of Science:

  • Computational chemistry
  • Materials science
  • Chemical physics

Background:

  • Crystalline nitromethane is a high-energy material sensitive to shock compression.
  • Understanding shock wave dynamics is crucial for predicting material behavior under extreme conditions.

Purpose of the Study:

  • To determine the relaxation rates of shocked crystalline nitromethane.
  • To investigate the thermal equilibration processes behind a shock wave.

Main Methods:

  • Molecular dynamics (MD) simulations were performed on (100)-oriented crystalline nitromethane.
  • The Sorescu-Rice-Thompson force field was employed to describe interatomic forces.
  • Analysis focused on kinetic energy distributions and covalent bond potentials.

Main Results:

  • Local temperatures of molecular center-of-mass and atomic kinetic energy distributions diverged rapidly.
  • Thermal equilibrium was established within several picoseconds.
  • Effective force constants for C-N, C-H, and N-O bonds increased significantly behind the shock front.

Conclusions:

  • Shock compression leads to distinct local temperatures that converge over picoseconds.
  • Covalent bonds in nitromethane become stiffer under shock compression.
  • The observed exponential relaxation suggests a well-defined process behind the shock wave.