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

Abstract

We present Born–Oppenheimer (BO) and Renner–Teller (RT) time dependent quantum dynamics studies of the reactions O(³P) + H₂⁺(X²Σ_g⁺) → OH⁺(X³Σ⁻) + H(²S) and OH(X²Π) + H⁺. We consider the OH₂^{+ 2}A′′ and òA′ electronic states that correlate with a linear ²Π species. The electronic angular momenta operators and ² are considered in nonadiabatic coupled-channel calculations, where the associated RT effects are due to diagonal V^RT potentials that add up to the PESs and to off-diagonal C^RT couplings between the potential energy surfaces (PESs). Initial-state-resolved reaction probabilities P_I, integral cross sections σ_I, and rate constants k_I are obtained using recent ab initio PESs and couplings and the real wavepacket formalism. Because the PESs are strongly attractive, P_I have no threshold energy and are large, σ_I decrease with collision energy, and k_I depend little on the temperature. The ²A′′ PES is up to three times more reactive than the òA′ PES and H₂⁺ rotational effects (j₀ = 0, 1) are negligible. The diagonal V^RT potentials are strongly repulsive at the collinearity and nearly halve all low-energy observables with respect to the BO ones. The off-diagonal C^RT couplings are important at low partial waves, where they mix the ²A′′ and òA′ states up to ∼20%. However, V^RT effects predominate over the C^RT ones that change at most by ∼19% the BO values of σ_I and k_I. The reaction O(³P) + H₂⁺(X²Σ_g⁺) → OH⁺(X³Σ⁻) + H(²S) is probably one of the most reactive atom + diatom collisions because its RT rate constant at room temperature is equal to 2.26 × 10⁻¹⁰ cm³ s⁻¹. Within the BO approximation, the present results agree rather well with recent quasiclassical and centrifugal-sudden data using the same PESs.