A globally accurate potential energy surface of $$\mathrm{HS_2}{(A\,^2A^\prime )}$$ HS 2 ( A 2 A ′ ) and studies on the reaction dynamic of $$\mathrm{H}(^2\mathrm{S})+\mathrm{S_2}(a\,^1{\varDelta }_g)$$ H ( 2 S ) + S 2 ( a 1 Δ g )

A new global analytical ab initio potential energy surface for the dynamics of the C+(2P) + SH(X2Π) reaction

The global potential energy surface (PES) of HCS⁺(X¹Σ⁺) is constructed using many-body expansion (MBE) methodology. The obtained analytical function is found by fitting the 7907 ab initio energy points computed at the Davidson-corrected multi-reference configuration interaction level with the aug-cc-pV(5+d)Z basis set. The final root mean square error is 0.0419 eV, and the maximum deviation is 0.2039 eV, showing that the analytical formula agrees well with the energy points. The topological features are calculated and discussed based upon the analytical PES of HCS⁺(X¹Σ⁺). The reaction probability, integral cross sections and other details of the C⁺(²P) + SH(X²Π) → H(²S) + CS⁺(X²Σ⁺) reaction are investigated using the quasi-classical trajectory and time-dependent quantum wave packet methods.

Quasi-Classical Trajectory Study of NH(3∑-) + NH(3∑-) Reactive Collisions

A full-dimension quasi-classical trajectory study of collisions between two NH radicals is presented. Interatomic interactions are represented by a previously reported global six-dimensional potential energy surface for singlet electronic state of the N₂H₂ system. This study suggests that the formation of N₂ from the collision of two NH radicals may occur via a one-step (NH + NH → N₂ + H + H) or two-step (NH + NH → N₂H + H → N₂ + H + H) microscopic reaction mechanism. A fast vibrational energy redistribution is observed in the four-body complex in the latter mechanism. Excitation functions are presented and discussed. A variant of the vibrational energy quantum mechanical threshold method was used to correct the zero-point energy leakage in the classical calculations. The influence of reactant's rotational and vibrational energy on reactivity was investigated by state-specific calculations with one or both reactants excited. Reaction rate constants for the ground and some rotationally excited states are presented using an Arrhenius-Kooij-like functional form.

Interaction and Photodissociation of Electronic Excited States of HS2 in the Ultraviolet Region: A Theoretical Contribution

HS₂ molecules play an important role in the photochemical processes in combustion, atmosphere, and interstellar medium, yet our knowledge about the electronic excited states in the UV region is limited. In this study, we perform high-level ab initio calculations on electronic states of HS₂ using the internally contracted multireference configuration interaction method including the Davidson correction (icMRCI + Q) method. The vertical transition energies, oscillator strengths, electron configurations, and transitions of thirteen electronic states of HS₂ with energy up to 8 eV are calculated at the icMRCI + Q/aug-cc-pv(5 + d)Z level. Based on the calculated potential energy curves, we investigate the interaction and photodissociation mechanism of the electronic states, which should shed some light on the decomposition processes of the gas-phase HS₂ molecules in the ultraviolet region.

Globally Accurate Potential Energy Surface for HCS(A2A″) by Extrapolation to the Complete Basis Set Limit

A global potential energy surface (PES) representation of the C(³P) + SH(X ²Π) → H(²S) + CS(a ³Π) system is developed by fitting plenty of precise energies obtained through the ab initio calculation with aug-cc-pV QZ and aug-cc-pV5Z basis sets via extrapolation to the complete basis set limit. The topographical characteristics of the PES are examined in detail, and it is found that they agree well with previous calculations available in the literature. By utilizing the PES of HCS(A²A″), the corresponding reaction is investigated using the quasi-classical trajectory (QCT) method in the collision energy range of 0.08-1.0 eV. The minimum energy paths (MEPs) calculated on the basis of the present PES indicate that the C(³P) + SH(X ²Π) → H(²S) + CS(a ³Π) reaction is exothermic, with the exothermicity ∼0.204 eV. The calculation for the capture time indicates that the reaction is mainly governed by the indirect mechanism at the lower collision energy, while, for higher collision energy, the direct mechanism is in coexistence with the indirect mechanism, and the latter one plays a dominant role.