Quasiclassical Trajectory Studies of State-Resolved Bimolecular Reactions: Vibrational Distributions in Triatomic Products

Abstract

This paper describes theoretical and computational research aimed at understanding the vibrational state distributions of triatomic molecule products which are produced in diatom plus diatom reactive collisions.The primary computational tool in this research is quasiclassical trajectories, wherein the vibrational states of the products are determined by numerically calculating the "good" actions associated with vibrational motion.Four exothermic reactions are considered: OH + Hz(Dz), H2+ + H2, OH + CO, and NH + NO. The first two of these reactions are direct reactions which produce nonlinear product triatomics while the second two involve the formation of short-lived complexes and linear product triatomics. Our analysis considers energy partitioning between vibration, translation, and rotation and state distributions associated with the vibrational modes. Common features among all the reactions are that bend modes excitation is significant and that stretch mode excitation is accompanied by significant bend excitation. None of the vibrational distributions are statistical, but only the HOD stretch modes in OH + DZ and the bend mode of COZ and N20 in OH + CO and NH + NO show easily understood mode-specific propensities.

A theoretical study of the NH+NO reaction

“…The HϩN 2 O results in Tables IV and V are in good agreement ͑for averaged quantities͒ with results for surface II that were presented in Ref. 32, so we defer to that paper for further discussion.…”

“…Some results for surface II were presented in another paper. 32 In Table IV, Q M gives the reactive cross section and ͗E trans ͘ M the average translational energy for product M, where MϭOHϩN 2 and HϩN 2 O. The energies in vibration and rotation of each diatomic product are denoted ͗E vib ͘ OH , ͗E rot ͘ OH , ͗E vib ͘ N 2 , and ͗E rot ͘ N 2 , and the corresponding triatomic energies are ͗E vib ͘ N 2 O and ͗E rot ͘ N 2 O .…”

The reactivity of ground-state carbon atoms with unsaturated hydrocarbons in combustion flames and in the interstellar medium

“…Quasiclassical trajectory (QCT) calculations are of particular signi®cance to investigate the e ects of the collision energy on the reaction dynamics and to derive scalar and vector properties [269,270]. These are, for instance, the cross-section as a function of the collision energy, the opacity function, the rovibrational distributions of the products of interest, the translational energy distribution P…E T †, the angular distribution T… † and the di erential cross-section as the intensity as a function of angle and product centre-of-mass velocity u.…”

A quasiclassical trajectory study of product state distributions from the CN+H2→HCN+H reaction

“…1,2 There is now a significant effort underway to extend these methodologies to larger polyatomic systems such as diatom-diatom reactions. 3 Yet, there are relatively few reports of computed product state distributions for diatom-diatom reactions from full dimensional models. Despite the fact that the quasiclassical trajectory method does not account for quantum effects and is subject to the problem of vibrational zero-point energy leakage, it is an attractive choice for initial calculations of this type because it is less computationally intensive than exact quantum treatments.…”