Collision-induced intramolecular energy flow and C–H bond dissociation in excited toluene

Energy flow and C-H methyl and C-H ring bond dissociations in vibrationally excited toluene in the collision with N 2 and O 2 have been studied by use of classical trajectory procedures. The energy lost by the vibrationally excited toluene upon collision is not large and it increases slowly with increasing total vibrational energy content between 5,000 and 45,000 cm −1 . Intermolecular energy transfer occurs via both of V-T and V-V transfers. Both of V-T and V-V transfers increase as the total vibrational energy of toluene increases. When the total energy content E T of toluene is sufficiently high, either C-H bond can dissociate. The C-H methyl dissociation probability is higher than the C-H ring dissociation probability, and that in the collision with N 2 is larger than with O 2 .

Section: Numerical Proceduresmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Energy Flow and Bond Dissociation of Vibrationally Excited Toluene in Collisions with N₂and O₂

Ree

Kim²,

Lee

2013

“…The initial conditions for the relative and vibrational motions in the interaction zone are given in Ref. 29. We sample 40,000 trajectories for each run at 300 K, where the sampling includes determining collision energies (E) sampled from the Maxwell distribution and weighting the initial vibrational and rotational energies by the Boltzmann distribution at 300 K.…”

Section: -46mentioning

confidence: 99%

“…[23][24][25][26][27][28][29][30][31] One such molecule is toluene, which contains two distinctly different C-H bonds, namely the methyl C-H and ring C-H bonds, along with many C-C bonds. When toluene undergoes a collision with other molecules, both intermolecular energy transfer and intramolecular energy flow from one CH bond to others via C-C bonds can occur.…”

Section: -13mentioning

confidence: 99%

Collision-induced Energy Transfer and Bond Dissociation in Toluene by H₂/D₂

Ree

Kim

Shin

2013

Energy transfer and bond dissociation of C-Hmethyl and C-Hring in excited toluene in the collision with H2 and D2 have been studied by use of classical trajectory procedures at 300 K. Energy lost by the vibrationally excited toluene to the ground-state H2/D2 is not large, but the amount increases with increasing vibrational excitation from 5000 and 40,000 cm −1. The principal energy transfer pathway is vibration to translation (V-T) in both systems. The vibration to vibration (V-V) step is important in toluene + D2, but plays a minor role in toluene + H2. When the incident molecule is also vibrationally excited, toluene loses energy to D2, whereas it gains energy from H2 instead. The overall extent of energy loss is greater in toluene + D2 than that in toluene + H2. The different efficiency of the energy transfer pathways in two collisions is mainly due to the near-resonant condition between D2 and C-H vibrations. Collision-induced dissociation of C-Hmethyl and C-Hring bonds occurs when highly excited toluene (55,000-70,400 cm) interacts with the ground-state H2/D2. Dissociation probabilities are low (10) but increase exponentially with rising vibrational excitation. Intramolecular energy flow between the excited C-H bonds occurring on a subpicosecond timescale is responsible for the bond dissociation.

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14] In recent years, furthermore, collisions involving large molecules have been studied actively, revealing valuable information on the rates and the mechanisms of vibrational energy processes. In particular, molecules vibrationally excited to near their dissociation threshold can undergo bond dissociation and vibrational relaxation, processes that play an important role in reaction dynamics.…”

mentioning

confidence: 99%

Collision-Induced Intramolecular Energy Flow in Highly Excited Toluene

2003

The collision-induced relaxation of vibrationally excited molecules has been the subject of continuing interest for the past several decades. [1][2][3][4][5][6][7][8][9][10][11][12][13][14] In recent years, furthermore, collisions involving large molecules have been studied actively, revealing valuable information on the rates and the mechanisms of vibrational energy processes. In particular, molecules vibrationally excited to near their dissociation threshold can undergo bond dissociation and vibrational relaxation, processes that play an important role in reaction dynamics. Recent studies 3,[5][6][7][8][9][10][11] show that when the excited molecule is a large organic molecule, the average amount of energy transfer per collision is not very large. The average energy transfer per collision between the highly vibrationally excited benzene and a noble gas atom is known to be about 30 cm, which is much smaller than benzene derivatives such as hexafluorobenzene or other hydrocarbons such as toluene and azulene.5,12-14 For example, for hexafluorobenzene + Ar, the measured value of the mean energy transfer per collision by the ultraviolet absorption method is −330 cm −1 , 13 whereas the calculated value using quasiclassical trajectory methods at 300 K is −150 cm . 14 These magnitudes are much larger in comparison to results for benzene colliding with argon. Among such large molecules, toluene is a particularly attractive molecule for studying collision-induced intramolecular energy flow and bond dissociation because of the presence of both methyl and ring CH bonds.In this paper, as an extension of th previous work in ref. 11, we study the collision-induced dynamics of highly vibrationally excited toluene interacting with argon using quasiclassical trajectory calculations. We now consider the collision system in which one CH (either CH methyl or CH ring ) vibration is in a highly excited state and the other in a ground state, while in Ref. 11 we considered both of CH methyl and CH ring bonds are in highly excited states. In the latter, it was not clear which CH bond is more effective for collisioninduced inter-and intra-molecular energy transfer in collision with Ar. Thus, we now elucidate which CH bond is more effective for collision-induced inter-and intra-molecular energy transfer, as considering and comparing the results of inter-and intra-molecular energy transfer dynamics when either CH methyl or CH ring is in highly excited states. Using the results obtained in the calculations, we discuss the relaxation of the excited CH vibration, and the time evolution of collision-induced intramolecular energy flow from the highly excited CH vibration. Thus, we elucidate the nature and mechanism of competition between methyl CH mode and ring CH mode in transferring energy to the incident atom. We set the initial vibrational energy of the methyl CH bond or the ring CH bond equal to the state just 0.10 eV below the dissociation threshold at 300 K. Interaction ModelThe present work follows the interaction model and numerical p...