Dynamics of the O + H₂⁺ → OH⁺ + H, OH + H⁺ proton and hydrogen atom transfer reactions on the two lowest potential energy surfaces

Abstract

The dynamics of the title reaction was studied using mainly the quasiclassical trajectory (QCT) method on the ground 1A'' (OH channel) and first excited 1A' (OH channel) potential energy surfaces (PESs) employing ab initio analytical representations of the PESs developed by us. Both PESs correspond to exoergic reactions, are barrierless and present a deep minimum along the minimum energy path (MEP). Some extra calculations (cross sections) were also performed with the time dependent quantum real wave packet method at the centrifugal sudden level (RWP-CS method). A broad set of properties as a function of collision energy (E ≤ 0.5 eV) was considered using the QCT method: cross sections, average fractions of energy, product rovibrational distributions, two- and three-vector properties, and the microscopic mechanisms analyzing their influence on the dynamics. The proton transfer channel dominates the reactivity of the system and significant differences between the two reaction channels are found for the vibrational distributions and microscopic mechanisms. The results were interpreted according to the properties of the ground and excited PESs. Moreover, the QCT and RWP-CS cross sections are in rather good agreement for both reaction channels. We hope that this study will encourage the experimentalists to investigate the dynamics of this interesting but scarcely studied system, whose two lowest PESs include the ground and first excited electronic states of the HO cation.

Born–Oppenheimer and Renner–Teller coupled-channel quantum reaction dynamics of O(3P) + H2+(X2Σg+) collisions

“…Fig. 8,9 These findings imply that O + H 2 + collisions are very reactive and that the H product channel (proton transfer reaction) is favored with respect to the H + one. At low J values, the BO probabilities (left panels) do not present any threshold and increase sharply up to high values, with mild oscillations around a value of B0.90.…”

“…We report initial-state-resolved integral cross sections and rate constants in Section IV, discussing the influence of the RT effects on both product channels and comparing our BO results with previous QCT 8, 9 and RWP CS 9 calculations and we, finally, present in Section V the main conclusions. Section II presents some theoretical and computational details, enlightening the origin, formulae, and physical meanings of the adiabatic (diagonal) and nonadiabatic (off diagonal) RT terms.…”

“…Moreover, the single-state dynamics is affected by the V RT potential (2.1) and the C RT couplings (2.2) vanish identically at J = 0, when the WP remains on the initial surface. 9 The energy thresholds depend on the BJ(J + 1) centrifugal barriers in the entrance valley and on the J-dependent energy shifts found on the à 2 A 0 excited surface, which correlates with the excited OH + H + products, are much larger than those found on the ground X 2 A 00 PES. 2 reports BO and RT reaction probabilities P JÀ X00 and P J+ A00 for both channels H and H + and initial electronic states, at J = 0, 10, and 50, p = À( 2 A 00 ) or +( 2 A 0 ), j 0 = 0, and K 0 = 0.…”

“…These two electronic states of H 2 O + correspond to the degenerate components of a 2 P u species, when the molecule is in a linear arrangement, and the associated nonadiabatic (NA) Renner-Teller (RT) effects can remarkably influence the dynamics of these collisions, as they also occur for the X 2 B 1 À Ã 2 A 1 optical spectrum 12 of H 2 + O. Following that work, Martínez et al 9 employed the quantum-mechanical real wavepacket (RWP) method to obtain BO centrifugal-sudden (CS) initial-state-selected reaction probabilities and cross sections. 8,9 When the RT interactions are large, we really have two coupled reactions (1.1) and (1.2) that mainly proceed on both interacting PESs.…”

“…16 and À7.54 eV with respect to the reactants. 8,9 When the RT interactions are large, we really have two coupled reactions (1.1) and (1.2) that mainly proceed on both interacting PESs. The ground PES (X 2 A 00 ) includes the ground electronic state of the water cation, H 2 O + (X 2 B 1 ), in the minimum energy path (MEP) connecting reactants and OH + + H products; while the first excited PES (Ã 2 A 0 ) includes the first excited electronic state of the water cation, H 2 O + (Ã 2 A 1 ), in the MEP involving reactants and OH + H + products.…”