## Abstract

Molecular dynamics simulations were used to study relaxation of a vibrationally excited C_{6}F_{6}* molecule in a N _{2} bath. Ab initio calculations were performed to develop N _{2}-N_{2} and N_{2}-C_{6}F_{6} intermolecular potentials for the simulations. Energy transfer from "hot" C_{6}F_{6} is studied versus the bath density (pressure) and number of bath molecules. For the large bath limit, there is no heating of the bath. As C_{6}F_{6}* is relaxed, the average energy of C_{6}F_{6}* is determined versus time, i.e., 〈E(t)〉, and for each bath density 〈E(t)〉 is energy dependent and cannot be fit by a single exponential. In the long-time limit C_{6}F_{6} is fully equilibrated with the bath. For a large bath and low pressures, the simulations are in the fixed temperature, independent collision regime and the simulation results may be compared with gas phase experiments of collisional energy transfer. The derivative d[〈E(t)〉]/ dt divided by the collision frequency ω of the N_{2} bath gives the average energy transferred from C_{6}F_{6}* per collision 〈ΔE_{c}〉, which is in excellent agreement with experiment. For the ∼100-300 ps simulations reported here, energy transfer from C_{6}F_{6}* is to N_{2} rotation and translation in accord with the equipartition model, with no energy transfer to N_{2} vibration. The energy transfer dynamics from C_{6}F _{6}* is not statistically sensitive to fine details of the N _{2}-C_{6}F_{6} intermolecular potential. Tests, with simulation ensembles of different sizes, show that a relatively modest ensemble of only 24 trajectories gives statistically meaningful results.

Original language | English |
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Article number | 194103 |

Journal | Journal of Chemical Physics |

Volume | 140 |

Issue number | 19 |

DOIs | |

State | Published - May 21 2014 |

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