A global coupled cluster potential energy surface for HCl + OH ↔ Cl + H₂O

Area of Science:

• Chemical Physics
• Atmospheric Chemistry
• Computational Chemistry

Background:

• The ClH2O system is crucial for understanding atmospheric reactions.
• Accurate potential energy surfaces (PES) are essential for chemical kinetics.
• Previous PES calculations had limitations in accuracy.

Purpose of the Study:

• To develop a new, highly accurate, full-dimensional global potential energy surface (PES) for the ground electronic state of the ClH2O system.
• To improve the characterization of the HCl + OH reaction kinetics.
• To investigate the impact of PES accuracy on quantum dynamical calculations.

Main Methods:

• Developed a new PES by fitting 15,777 points using an explicitly correlated unrestricted coupled-cluster method with single, double, and perturbative triple excitations (UCCSD(T)-F12b).
• Employed the permutation invariant polynomial-neural network (PIP-NN) method for PES fitting, achieving an error of 6.9 meV.
• Performed quantum dynamical calculations of reaction probabilities for forward and reverse reactions on the new PES.

Main Results:

• The new PES features a slightly lower reaction barrier for HCl + OH → Cl + H2O compared to previous multi-reference configuration interaction (MRCI) based PES.
• Quantum dynamical calculations on the new PES reveal notable differences in reaction probabilities compared to calculations on the MRCI PES.
• The improved accuracy of the new PES is expected to enhance the characterization of reaction kinetics.

Conclusions:

• The developed PIP-NN based PES provides a more accurate representation of the ClH2O system's ground electronic state.
• The subtle differences in PESs significantly impact quantum dynamical calculations, highlighting the importance of PES accuracy.
• This work offers a refined tool for studying atmospheric reaction mechanisms involving chlorine and hydroxyl radicals.