The hydroperoxy radical as a hydrogen bond acceptor. HOO-HCl complexes--Ab initio study

Area of Science:

• Physical Chemistry
• Quantum Chemistry
• Computational Chemistry

Background:

• Previous investigations suggested three potential protonation sites on the HOO radical.
• Topological methods like Atoms in Molecules (AIM) and Electron Localization Function (ELF) were used to analyze HOO radical properties.

Purpose of the Study:

• To investigate the protonacceptor properties of the HOO radical.
• To confirm and characterize the 1:1 complexes formed by HCl and HOO molecules.
• To simulate harmonic and anharmonic spectra of these complexes.

Main Methods:

• Ab initio calculations
• Topological analysis (AIM, ELF)
• Structure optimization
• Numerical diagonalization of a one-dimensional Hamiltonian for anharmonic spectra simulation

Main Results:

• Three distinct 1:1 complexes of HCl and HOO were identified, corresponding to local minima.
• The cyclic structure was found to be the most stable complex.
• Anharmonic spectra simulation, particularly of the H-Cl stretching vibration, characterized the Cl-H...O hydrogen bond.

Conclusions:

• The study fully confirms previous suppositions about the protonation sites and complex structures.
• The cyclic complex is the most stable, aligning with experimental findings.
• MP2 level calculations accurately predict spectral properties, while B3LYP is unsuitable for this PES investigation.