Bath Model for N2 + C6F6 Gas-Phase Collisions. Details of the Intermolecular Energy Transfer Dynamics

Abstract

Relaxation of vibrationally excited C6F6* in a thermalized bath of N2 molecules is studied by condensed-phase chemical dynamics simulations. The average energy of C6F6 as a function of time, ⟨E(t)⟩, was determined using two different models for the N2–C6F6 intermolecular potential, and both gave statistically the same result. A simulation with a N2 bath density of 20 kg/m3 was performed to check the convergence and validate the results obtained previously with a higher bath density of 40 kg/m3. The initial ensemble of C6F6 is nearly monoenergetically excited, but the ensemble acquires as energy distribution P(E) as it is collisionally relaxed. An evaluation of P(E) and the root-mean-square deviation ⟨ΔE2⟩1/2 of P(E), versus time, shows that P(E) first broadens and then narrows. Simulations with the C6F6 vibrational excitation energy of 85.8 kcal/mol, studied experimentally, show that the width of P(E) does not affect the average collisional deactivation rate. The role of the intramolecular vibrational fre...