Advances and New Challenges to Bimolecular Reaction Dynamics Theory

Abstract

Dynamics of bimolecular reactions in the gas phase are of foundational importance in combustion, atmospheric chemistry, interstellar chemistry, and plasma chemistry. These collision-induced chemical transformations are a sensitive probe of the underlying potential energy surface(s). Despite tremendous progress in past decades, our understanding is still not complete. In this Perspective, we survey the recent advances in theoretical characterization of bimolecular reaction dynamics, stimulated by new experimental observations, and identify key new challenges.

Full-dimensional quantum stereodynamics of the non-adiabatic quenching of OH(A2Σ+) by H2

“…Although the Born–Oppenheimer approximation 1 , which assumes separability of nuclear and electronic motion, is widely accepted for characterizing reactions in their ground electronic states, there is general agreement that dynamics can be impacted by excited electronic states near an electronic degeneracy, such as conical intersections (CI), where the electronic and nuclear coordinates are strongly coupled. While ultrafast non-adiabatic transitions near a CI have been extensively studied in photochemistry 2 – 8 and non-reactive collisions 9 – 11 , fewer studies on non-Born–Oppenheimer effects exist for bimolecular reactions 12 . Existing first-principles theories of non-adiabatic reaction dynamics mostly deal with open-shell atoms, focusing on geometric phase effects 13 – 15 or spin–orbit excited electronic states 16 – 21 .…”

“…These high-quality DPEMs have opened the door for dynamical studies 40 – 42 , 45 . While the non-adiabatic dynamics can only be accurately characterized quantum mechanically, such calculations are challenging because of the large energy release (>4 eV), large accessible phase space and complex multistate dynamics 12 , 40 . So far, detailed quantum dynamics calculations have been restricted to planar geometries with two electronic states 41 , 45 .…”

Stereodynamical Control of Nonadiabatic Quenching Dynamics of OH(A2S+) by H2: Full-Dimensional Quantum Dynamics

“…While ultrafast nonadiabatic transitions near conical intersections (CIs) have been intensively studied in photochemistry, [2][3][4][5][6][7][8] non-BO effects have seldom been investigated in detail for collisions and bimolecular reactions. 9 Existing rst-principles theory of nonadiabatic reaction dynamics have mostly dealt with open-shell atoms, focusing on geometric phase effects [10][11][12] or spin-orbit excited electronic states. [13][14][15][16][17][18] In the present work, we extend the detailed rst-principles theory to the collision of electronically excited molecules, namely the hydroxyl radical in the OH(A 2 Σ + ) state, by studying the following processes in full dimensionality: OH(A 2 Σ + ) + H 2 → H + H 2 O (reactive quenching) (R1a) → OH(X 2 Π) + H 2 (non-reactive quenching) (R1b) → OH(A 2 Σ + ) + H 2 (elastic and inelastic scattering) (R1c)…”

“…[36][37][38]42 While the dynamics can only be accurately characterized quantum mechanically, such calculations are challenging because of the large energy release (> 4 eV), a large accessible phase space, and the complex multi-state dynamics. 9 Until now, quantum dynamics calculations have been restricted to planar geometries with two electronic states. 37,42 However, such a model is insu cient 38 since it neglects the 2 2 A state and important nonplanar dynamics.…”

Determination of Kinetic Properties in Unimolecular Dissociation of Complex Systems from Graph-Theory Based Analysis of an Ensemble of Reactive Trajectories.

“…For example, uni-and bi-molecular reaction dynamics simulations were largely studied with the aim of understanding several processes, from combustion to atmospheric chemistry, from interfacial reactions to photolysis or astrochemistry. [14][15][16][17][18][19][20] Unimolecular reactivity represents an important class of reactions, 21 with a relevant application in the field of mass spectrometry. 22 Recently, trajectories-based methods were used to understand several gas-phase ion chemistry experiments, like electron ionization mass spectrometry, [23][24][25] surface-induced dissociation (SID) 6,26,27 or collision-induced dissociation.…”