Classical trajectory studies of the reaction CH4+H→CH3+H2

Abstract

Articles you may be interested inMode specific dynamics of the H2 + CH3 → H + CH4 reaction studied using quasi-classical trajectory and eightdimensional quantum dynamics methods J. Chem. Phys. 143, 154307 (2015) Trajectory data are reported for the reaction CH 4 ϩH→CH 3 ϩH 2 , designed to provide information that can be used to test approximate quantitative theories for the dynamics of abstraction reactions. A potential function was devised which properly reflects the nuclear permutation symmetry of the process. Microscopic reaction rate coefficients were obtained as functions of fixed rotational and vibrational energy, and of the angular momentum. The data indicated significant uncoupling between the various modes although, at a minimum, the symmetric stretch is directly coupled to the reaction coordinate at the transition state. The data were used to test the assumption that the total angular momentum, J, may be approximated by the orbital angular momentum, L. L is approximately conserved from the reactant to the saddle point configuration in reactive and nonreactive collisions and may be well approximated by J. The angular momentum about the long axis of the reacting system ͑equivalent to the K quantum number͒ is not conserved in either reactive or nonreactive trajectories.

QM/MM: what have we learned, where are we, and where do we go from here?

“…It is much harder to treat synchronous bond breaking and bond forming, but this was also accomplished in the early days of quantum mechanics, resulting in the London equation [186][187][188]. Raff [189] was apparently the first to combine the valence-bond-derived QM London equation with molecular mechanics terms to make a QM/MM reactive potential, and in recent years many other workers, [190,191] especially Espinosa-Garcia and coworkers [192][193][194][195][196][197], have made fruitful use of this technique. Various workers, of whom we single out Brenner [198][199][200] and Goddard and coworkers [201][202][203][204] for noteworthy systematic efforts, have made generalizations to more complex reactive systems.…”

Accurate calculations of reaction rates: predictive theory based on a rigorous quantum transition state concept

“…Since reactive and vibrational motion in the barrier region are usually strongly coupled, descriptions beyond the most simple harmonic approximation require truly multi-dimensional quantum dynamics calculations. Here it was found that the anharmonicities in principle have a sizeable effect on the zero point energies (e.g., around 0.5 kcal/mol for CH 4 [69,99] and the H +CH 4 transition state [70] at the Jordan-Gilbert PES [72]), but these effects cancel out quite well when the differences between the transition state energies and the reactant energies are considered [69,70]. Thus, approximate calculations can typically disregard such anharmonic effects as long as it is consistently done in the reactant partition function and the N (E) computation.…”

“…While the above calculations could treat the quantum dynamics of the reaction process rigorously, still the underlying PES used in these calculations [72,73] were not accurate and resulted in significant differences between experiment and theory. Therefore the further development considered the construction of accurate full-dimensional PES which will be discussed in some more detail in Sect.3.…”

RPMDrate: Bimolecular chemical reaction rates from ring polymer molecular dynamics

“…In the test calculations reported below we used the BoothroydKeogh-Martin-Peterson (BKMP2) potential energy surface for H + H 2 [47], the modified and recalibrated versions of the JordanGilbert [48] potential energy surface developed by EspinosaGarcía et al for H + CH 4 [49] and OH + CH 4 [50], and the combined valence bond-molecular mechanics (CVBMM) potential energy surface for H + C 2 H 6 [51]. (The last three potential energy surfaces were taken from the online POTLIB library [52].)…”