Non-statistical intermolecular energy transfer from vibrationally excited benzene in a mixed nitrogen-benzene bath

Abstract

A chemical dynamics simulation was performed to model experiments [N. A. West et al., J. Chem. Phys. 145, 014308 (2016)] in which benzene molecules are vibrationally excited to 148.1 kcal/mol within a N2-benzene bath. A significant fraction of the benzene molecules are excited, resulting in heating of the bath, which is accurately represented by the simulation. The interesting finding from the simulations is the non-statistical collisional energy transfer from the vibrationally excited benzene C6H6* molecules to the bath. The simulations find that at ∼10−7 s and 1 atm pressure there are four different final temperatures for C6H6* and the bath. N2 vibration is not excited and remains at the original bath temperature of 300 K. Rotation and translation degrees of freedom of both N2 and C6H6 in the bath are excited to a final temperature of ∼340 K. Energy transfer from the excited C6H6* molecules is more efficient to vibration of the C6H6 bath than its rotation and translation degrees of freedom, and the final vibrational temperature of the C6H6 bath is ∼453 K, if the average energy of each C6H6 vibration mode is assumed to be RT. There is no vibrational equilibration between C6H6* and the C6H6 bath molecules. When the simulations are terminated, the vibrational temperatures of the C6H6* and C6H6 bath molecules are ∼537 K and ∼453 K, respectively. An important question is the time scale for complete energy equilibration of the C6H6* and N2 and C6H6 bath system. At 1 atm and 300 K, the experimental V-T (vibration-translation) relaxation time for N2 is ∼10−4 s. The simulation time was too short for equilibrium to be attained, and the time for complete equilibration of C6H6* vibration with translation, rotation, and vibration of the bath was not determined.

A Better Understanding of the Unimolecular Dissociation Dynamics of Weakly Bound Aromatic Compounds at High Temperature: A Study on C6H6–C6F6 and Comparison with C6H6 Dimer

“…The parameters for the intramolecular potential energy function are obtained from the literature 38 and are also tested in previous works. 39,40 The equilibrium bond lengths r e , bond angles θ e , force constants for stretching f s , bending f θ , and wagging f α , and the torsional barriers V 0 for benzene and HFB are listed in Table 1. A Morse potential energy of the form The Bz−HFB intermolecular potential is represented by the OPLS-AA model, 41 for which the potential energy is written as a sum of two-body terms, i.e.…”

Mode‐specific pressure effects on the relaxation of an excited nitromethane molecule in an argon bath

“…Recent molecular dynamics studies [8][9][10][11][12][13][14][15][16][17] of excited molecules in a pressurized bath gas include excited diatomic molecules OH, 17 triatomic molecules HO 2 , 13 and polyatomic molecules CH 3 NO 2 , 10 C 6 H 6 , 16 C 6 F 6 , 8,9,12 C 10 H 8 , 11 and C 9 H 12 + . 14,15 The pressurized bath gases include He, 14 Ar, 10,13,17 and N 2 .…”

“…14,15 The pressurized bath gases include He, 14 Ar, 10,13,17 and N 2 . 8,9,11,12,15,16 In these studies, the breakdown in the IBC approximation, as determined by the deviation of relaxation rates from a linear dependence on pressure, has ranged from 35 to over 400 atm for vibrational relaxation. Of particular relevance to this study is the CH 3 NO 2 /Ar molecular dynamics study of Rivera-Rivera et al 10 (henceforth RWST) mentioned above.…”

“…Recent molecular dynamics studies 8–17 of excited molecules in a pressurized bath gas include excited diatomic molecules OH, 17 triatomic molecules HO 2 , 13 and polyatomic molecules CH 3 NO 2 , 10 C 6 H 6 , 16 C 6 F 6 , 8,9,12 C 10 H 8 , 11 and C 9 H 12 + 14,15 . The pressurized bath gases include He, 14 Ar, 10,13,17 and N 2 8,9,11,12,15,16 . In these studies, the breakdown in the IBC approximation, as determined by the deviation of relaxation rates from a linear dependence on pressure, has ranged from 35 to over 400 atm for vibrational relaxation.…”

Pressure Effects on the Relaxation of an Excited Ethane Molecule in High-Pressure Bath Gases

“…Recent molecular dynamics studies of excited molecules in high-pressure bath gases include excited C 6 F 6 molecule in an N 2 bath − at 298 K at pressures of 15–710 atm, excited CH 3 NO 2 in an Ar bath at 300 K at pressures of 10–400 atm, excited C 10 H 8 in an N 2 bath at 298 K at pressures of 9–70 atm, excited HO 2 radical in an Ar bath at 800 K at pressures of 10–400 atm, excited C 9 H 12 + at 473 K in a He bath (100–775 atm) and in an N 2 bath (14–440 atm), excited C 6 H 6 in an N 2 bath at 300 K at a pressure of 35 atm, and excited OH radical in an Ar bath at 300 K at pressures of 50–400 atm. Additionally, there has been a study of thermally cold C 6 F 6 in a 300 K N 2 bath at pressures of 18–70 atm.…”