## Abstract

Classical chemical dynamics simulations were performed to study the intramolecular and unimolecular dissociation dynamics of the benzene dimer, Bz_{2} → 2 Bz. The dissociation of microcanonical ensembles of Bz_{2} vibrational states, at energies E corresponding to temperatures T of 700-1500 K, were simulated. For the large Bz_{2} energies and large number of Bz_{2} vibrational degrees of freedom, s, the classical microcanonical (RRKM) and canonical (TST) rate constant expressions become identical. The dissociation rate constant for each T is determined from the initial rate dN(t)/dt of Bz_{2} dissociation, and the k(T) are well-represented by the Arrhenius eq k(T) = A exp(-E_{a}/RT). The E_{a} of 2.02 kcal/mol agrees well with the Bz_{2} dissociation energy of 2.32 kcal/mol, and the A-factor of 2.43 × 10^{12} s^{-1} is of the expected order-of-magnitude. The form of N(t) is nonexponential, resulting from weak coupling between the Bz_{2} intramolecular and intermolecular modes. With this weak coupling, large Bz_{2} vibrational excitation, and low Bz_{2} dissociation energy, most of the trajectories dissociate directly. Simulations, with only the Bz_{2} intramolecular modes excited at 1000 K, were also performed to study intramolecular vibrational energy redistribution (IVR) between the intramolecular and intermolecular modes. Because of restricted IVR, the initial dissociation is quite slow, but N(t) ultimately becomes exponential, suggesting an IVR time of 20.7 ps.

Original language | English |
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Pages (from-to) | 6631-6640 |

Number of pages | 10 |

Journal | Journal of Physical Chemistry A |

Volume | 119 |

Issue number | 25 |

DOIs | |

State | Published - Jun 25 2015 |