Long Range Collisional Energy Transfer from Highly Vibrationally Excited Pyrazine to CO Bath Molecules:  Excitation of the v = 1 CO Vibrational Level

Classical trajectory calculations were performed to simulate state-resolved energy transfer experiments of highly vibrationally excited pyrazine (E(vib) = 37,900 cm(-1)) and CO(2), which were conducted using a high-resolution transient infrared absorption spectrometer. The goal here is to use classical trajectories to simulate the supercollision energy transfer pathway wherein large amounts of energy are transferred in single collisions in order to compare with experimental results. In the trajectory calculations, Newton's laws of motion are used for the molecular motion, isolated molecules are treated as collections of harmonic oscillators, and intermolecular potentials are formed by pairwise Lennard-Jones potentials. The calculations qualitatively reproduce the observed energy partitioning in the scattered CO(2) molecules and show that the relative partitioning between bath rotation and translation is dependent on the moment of inertia of the bath molecule. The simulations show that the low-frequency modes of the vibrationally excited pyrazine contribute most to the strong collisions. The majority of collisions lead to small DeltaE values and primarily involve single encounters between the energy donor and acceptor. The large DeltaE exchanges result from both single impulsive encounters and chattering collisions that involve multiple encounters.

Section: Introductionsupporting

confidence: 75%

Trajectory Study of Supercollision Relaxation in Highly Vibrationally Excited Pyrazine and CO₂

Sansom

Bonella

et al. 2005

“…The model systems chosen for study are pyrazine + Ar and ethane + Ar. In its ground electronic state, pyrazine is approximately an oblate symmetric top and has been the subject of numerous energy transfer experiments ,− and several previous QCT studies. ,− Ethane, a prolate symmetric top, has been a benchmark for experimental and theoretical studies of unimolecular and recombination reactions. ,, It has also been used for QCT studies of energy transfer. ,, …”

Section: Introductionmentioning

confidence: 99%

Collisional Energy Transfer Probability DensitiesP(E,J;E′,J′) for Monatomics Colliding with Large Molecules

Barker

Weston

2010

Collisional energy transfer remains an important area of uncertainty in master equation simulations. Quasi-classical trajectory (QCT) calculations were used to examine the energy transfer probability density distribution (energy transfer kernel), which depends on translational temperature, on the nature of the collision partners, and on the initial and final total internal energies and angular momenta: P(E, J; E', J'). For this purpose, model potential energy functions were taken from the literature or were formulated for pyrazine + Ar and for ethane + Ar collisions. For each collision pair, batches of 10(5) trajectories were computed with three selected initial vibrational energies and five selected values for initial total angular momentum. Most trajectories were carried out with relative translational energy distributions at 300 K, but some were carried out at 1000 or 1200 K. In addition, some trajectories were computed for artificially "heavy" ethane, in which the H-atoms were assigned masses of 20 amu. The results were binned according to (ΔE, ΔJ), and a least-squares analysis was carried out by omitting the quasi-elastic trajectories from consideration. By trial-and-error, an empirical function was identified that fitted all 45 batches of trajectories with moderate accuracy. The results reveal significant correlations between initial and final energies and angular momenta. In particular, a strong correlation between ΔE and ΔJ depends on the smallest rotational constant in the excited polyatomic. These results show that the final rotational energy distribution is not independent of the initial distribution, showing that the plausible simplifying assumption described by Smith and Gilbert [Int. J. Chem. Kinet. 1988, 20, 307-329] and extended by Miller, Klippenstein, and Raffy [J. Phys. Chem. A 2002, 106, 4904-4913] is invalid for the systems studied.

“…With some modeling, the P ( E , E ‘) function (or at least its higher energy tail) can be extracted from the experiments − ,− more recent studies have investigated cold collision partners CO, , H 2 O, , and DCl …”

Section: Introductionmentioning

confidence: 99%

“…With some modeling, the P(E,E′) function (or at least its higher energy tail) can be extracted from the experiments. 41 Extensive work has been carried out studying relaxation of hot pyrazine by collision with CO 2 ; [34][35][36][37][38][39][42][43][44][45][46] more recent studies have investigated cold collision partners CO, 40,47 H 2 O, 48, 49 and DCl. 50 There is a long history of using classical trajectory methods to explore these systems: major contributions have been made by Gilbert, Lim and co-workers, [51][52][53][54][55][56] Lenzer, Luther, and coworkers, [57][58][59][60] and Bershtein, Oref and co-workers, [61][62][63][64][65][66][67] and others.…”

Section: Introductionmentioning

confidence: 99%

Collisional Energy Transfer between Hot Pyrazine and Cold CO: A Classical Trajectory Study

Higgins

Chapman

2004

Vibrational energy transfer from hot pyrazine (E′ ) 40 322 cm -1 ) to cold CO is modeled using classical trajectories. Collisional energy transfer properties are studied as a function of the initial rotational state J′ of the CO, the length of the CO, the energy E′ in pyrazine, the relative kinetic energy, the temperature, isotopic substitution on pyrazine, and the intermolecular potential. The energy transfer probability function P(E,E′) exhibits distinct deviation from single exponential behavior. Collisions that transfer particularly large energy are associated with large amplitude out-of-plane motion of a C-H bond, imparting a kick to the departing CO. Slower collisions are particularly effective in relaxing pyrazine; faster collisions can add energy as often as they remove it. Energy transfer properties also depend on the initial rotational state of the CO. Temperature effects on 〈E -E′〉 are weak in the 200-500 K range; this results from an increase in the magnitudes of both 〈∆E〉 down and 〈∆E〉 up . The fraction of pyrazine energy partitioned to translation increases with temperature. Decreasing the rotational temperature of pyrazine (at fixed translational temperature) decreases -〈E -E′〉 significantly. Decreasing translational temperature (at fixed pyrazine rotational temperature) increases -〈E -E′〉. This is in contrast to the conventional expectation, based on Landau-Teller theory. Effects of making modest changes of the intermolecular potential are also discussed. † Part of the special issue "Richard Bersohn Memorial Issue".