Global analytical potential energy surfaces for HO2(X2A") based on high-level ab initio calculations

Area of Science:

• Theoretical Chemistry
• Chemical Physics
• Computational Chemistry

Background:

• The hydroperoxyl radical (HO2) is a key intermediate in combustion and atmospheric chemistry.
• Accurate potential energy surfaces (PES) are crucial for understanding HO2 reaction dynamics and spectroscopy.
• Previous PES may lack accuracy in specific energy ranges relevant to vibrational spectra and reaction pathways.

Purpose of the Study:

• To develop two global analytical potential energy surfaces (PES) for the HO2(X2A") system.
• To create one PES optimized for accurate vibrational spectrum calculations.
• To create a second PES optimized for fast and uniformly accurate reaction dynamics simulations.

Main Methods:

• Approximately 15,000 ab initio points were calculated at the icMRCI+Qaug-cc-pVQZ level of theory.
• The reproducing kernel Hilbert space (RKHS) method was employed for fitting the ab initio data.
• Developed two analytical PES: one for vibrational spectroscopy, another for reaction dynamics.

Main Results:

• The developed analytical PES show good agreement with previous spline-fitted potentials for J=0 HO2 vibrational spectra.
• Calculated J=0 quantum reaction probabilities for H+O2(jii=0,nui=0) align well with results from the spline-fitted potential.
• Quasiclassical trajectory calculations on the new PES yield reaction probabilities at zero impact parameter in good agreement with quantum results.

Conclusions:

• The new analytical potential energy surfaces provide accurate representations for both the low-energy vibrational spectrum and reaction dynamics of the HO2 system.
• These PES are suitable for detailed theoretical studies of HO2 chemistry, including spectroscopy and reaction kinetics.