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

Amit K. Paul, Swapnil C. Kohale, William L. Hase

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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 frequencies on the energy transfer dynamics was studied by changing the mass of the F-atoms of C6F6 to that of an H-atom. The resulting increase in the frequencies decreased the efficiency of collisional energy transfer. Simulations with classical and quantum microcanoical ensembles of the C6F6 initial vibrational energy were compared, and the initial relaxation rate was slower for the quantum ensemble.

Original languageEnglish
Pages (from-to)14683-14691
Number of pages9
JournalJournal of Physical Chemistry C
Volume119
Issue number26
DOIs
StatePublished - Apr 9 2015

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