A Competition between Dissociation Pathway and Energy Transfer Pathway: Unimolecular Dissociation of a Benzene–Hexafluorobenzene Complex in Nitrogen Bath

Abstract

The unimolecular dissociation of a benzene− hexafluorobenzene complex at 1000, 1500, and 2000 K is studied inside a bath of 1000 N 2 molecules kept at 300 K using chemical dynamics simulation. Three bath densities of 20, 324, and 750 kg/ m 3 are considered. The dissociation dynamics of the complex at a 20 kg/m 3 bath density is found to be similar to that in the gas phase, whereas the dynamics is drastically different at higher bath densities. The microcanonical/canonical dissociation rate constants for the three bath densities are calculated and fitted to the Arrhenius equation. The activation energies are found to be similar to the gasphase one. However, the pre-exponential factor is lower and decreases with the increase in bath density. The vibrational degree of freedom of the complex more effectively participates in the collisional energy transfer to the N 2 bath, whereas the translational and rotational degrees of freedom of N 2 receive the transferred energy. The energy transfer efficiency increases with the increase in bath density. The time scale of the energy transfer pathway is more than that of the dissociation pathway, and negligible direct dissociation of the complex is observed from the simulation at the highest bath density.

Mode‐to‐Mode Collision Energy Transfer from Vibrationally Excited C6F6 to NO/N2 Mixed Bath with the Development of New Potential Energy Functions

“…As found in the previous simulations, [40][41][42][43][44][45][46][47] the average energy of HFB* versus time is fitted well with a biexponential function of the form…”

“…All the components of bath molecules are then placed simultaneously one after another in the box at random places. This is different than what was implemented before, [40][41][42][43][44][45][46][47] where the molecules were placed column-wise in a regular fashion. In the process of placing the bath molecule randomly, the overlap between the subjected molecule and any other molecule already present in the bath is avoided.…”

“…These indexes are used to read the atomatom potential energy parameters for all intramolecular and intermolecular interactions. On the contrary, in the previous version, [40][41][42][43][44][45][46][47] the potential energy parameters were defined by the atomic masses, which would have taken N (of NO)À N (of N 2 ) interactions the same as N (of N 2 )À N (of N 2 ) in the present simulations. Therefore, the current setup is more sophisticated than the previous one.…”

“…The parameters A, B, b, C, c, n, D, d, and m are obtained from the literature [40] and used in a number of simulations in the past. [40][41][42][44][45][46][47]…”

“…These studies include a recently developed bath model where a single excited molecule is surrounded by many thermalized bath molecules in a simulation box and IET was studied between the excited and the bath molecules. [40][41][42][43][44][45][46][47][48][49] In a seminal work, [40] the IET was studied for C 6 F 6 * + N 2 system, where a highly vibrationally excited hexafluorobenzene (HFB) was placed in a N 2 bath with 1000 N 2 molecules equilibrated at a temperature of 300 K. In that study, a single collisional bath density (pressure) was obtained which represented gas phase bi-molecular collisional limit. Also studied was the mode specific energy transfer efficiencies for both the excited molecule as well as the bath.…”