Nonadiabatic state-to-state reactive collisions among open shell reactants with conical intersections: the OH((2)Pi) + F((2)P) example

Accurate High-Level Ab Initio-Based Global Potential Energy Surface and Quantum Dynamics Calculation for the First Excited State of CH2. J Phys Chem A 2021;125:5490-5498. [PMID: 34137628 DOI: 10.1021/acs.jpca.1c02413]

A full three-dimensional global potential energy surface (PES), covering the whole configuration space, is reported first for the title system by fitting high-level ab initio energies at the multireference configuration interaction level with the aug-cc-pV6Z basis set. In this work, the many-body expansion method is invoked to fit the innate character of the CH₂⁺(1²A″) PES. The topographical features are examined in detail based on the new global PES and in accordance with the other calculations from the ab initio energies, which show the correct behavior at the C⁺(²P) + H₂(X¹Σ_g⁺) and CH⁺(a³Π) + H(²S) dissociation limits. Using a time-dependent wave packet method, we provide insights into the dynamics behavior for reaction of C⁺(²P) + H₂(X¹Σ_g⁺) → CH⁺(a³Π) + H(²S). The integral cross sections and reaction probabilities increase monotonically in terms of the collision energy.

Quantum and quasi-classical calculations for the S⁺ + H₂(v,j) → SH⁺(v',j') + H reactive collisions

State-to-state cross-sections for the S(+) + H2(v,j) → SH(+)(v',j') + H endothermic reaction are obtained using quantum wave packet (WP) and quasi-classical (QCT) methods for different initial ro-vibrational H2(v,j) over a wide range of translation energies. The final state distribution as a function of the initial quantum number is obtained and discussed. Additionally, the effect of the internal excitation of H2 on the reactivity is carefully studied. It appears that energy transfer among modes is very inefficient that vibrational energy is the most favorable for the reaction, and rotational excitation significantly enhances the reactivity when vibrational energy is sufficient to reach the product. Special attention is also paid to an unusual discrepancy between classical and quantum dynamics for low rotational levels while agreement improves with rotational excitation of H2. An interesting resonant behaviour found in WP calculations is also discussed and associated with the existence of roaming classical trajectories that enhance the reactivity of the title reaction. Finally, a comparison with the experimental results of Stowe et al. for S(+) + HD and S(+) + D2 reactions exhibits a reasonably good agreement with those results.

Quantum mechanical calculations of state-to-state cross sections and rate constants for the F + DCl → Cl + DF reaction

We present accurate state-to-state quantum wave packet calculations of integral cross sections and rate constants for the title reaction. Calculations are carried out on the best available ground 1(2)A' global adiabatic potential energy surface of Deskevich et al. [J. Chem. Phys. 124, 224303 (2006)]. Converged state-to-state reaction cross sections have been calculated for collision energies up to 0.5 eV and different initial rotational and vibrational excitations, DCl(v = 0, j = 0 - 1; v = 1, j = 0). Also, initial-state resolved rate constants of the title reaction have been calculated in a temperature range of 100-400 K. It is found that the initial rotational excitation of the DCl molecule does not enhance reactivity, in contract to the reaction with the isotopologue HCl in which initial rotational excitation produces an important enhancement. These differences between the isotopologue reactions are analyzed in detail and attributed to the presence of resonances for HCl(v = 0, j), absent in the case of DCl(v = 0, j). For vibrational excited DCl(v = 1, j), however, the reaction cross section increases noticeably, what is also explained by another resonance.

Wave packet calculations on nonadiabatic effects for the O(3P)+HF(1Σ+) reaction under hyperthermal conditions

We present wave packet calculations of total and state-to-state reaction probabilities and integral cross sections for the nonadiabatic dynamics of the O((3)P)+HF → F((2)P)+OH((2)Π) reaction at hyperthermal collision energies ranging from 1.2 to 2.4 eV. The validity of the centrifugal sudden approximation is discussed for the title reaction and a comprehensive investigation of the influence of nonadiabatic effects on the dynamics of this reactive system at high (hyperthermal) collision energies is presented. In general, nonadiabatic effects are negligible for averaged observables, such as total reaction probabilities and integral cross sections, but they are clearly observed in detailed observables such as rotationally state-resolved reaction probabilities. A critical discussion of nonadiabatic effects on the dynamics of the title reaction is carried out by comparing with the reverse reaction and the characteristics of the adiabatic and diabatic potential energy surfaces involved.

Accurate quantum wave packet calculations for the F + HCl → Cl + HF reaction on the ground 1(2)A' potential energy surface

We present converged exact quantum wave packet calculations of reaction probabilities, integral cross sections, and thermal rate coefficients for the title reaction. Calculations have been carried out on the ground 1(2)A' global adiabatic potential energy surface of Deskevich et al. [J. Chem. Phys. 124, 224303 (2006)]. Converged wave packet reaction probabilities at selected values of the total angular momentum up to a partial wave of J = 140 with the HCl reagent initially selected in the v = 0, j = 0-16 rovibrational states have been obtained for the collision energy range from threshold up to 0.8 eV. The present calculations confirm an important enhancement of reactivity with rotational excitation of the HCl molecule. First, accurate integral cross sections and rate constants have been calculated and compared with the available experimental data.

EFFECT OF THE REACTANT ALIGNMENT ON STEREODYNAMICS FOR THE REACTION F + OH

Quasi-classical trajectory (QCT) calculations are performed for the reaction F + OH → HF + O based on the adiabatic potential-energy surface (PES) of the 13A″ triplet state. The reaction probability as a function of incident angle has been presented. The differential cross sections (DCSs), the distribution of angle between k and j′, P(θr) and the distribution of dihedral angle denoting k – k′ – j′ correlation, P(ϕr) have also been calculated at the different incident angles in the center-of-mass (CM) frame, respectively. The effects of reactant alignment on stereodynamics of the reaction are firstly revealed, which provides the theoretical foundation for the related experiment and enriches the theories of the stereodynamics.