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Internal rotation in peroxynitrous acid (ONOOH).
Mark P McGrath1, F Sherwood Rowland
1Department of Chemistry, University of California, Irvine, CA 92697, USA. mpmcgrat@uci.edu
The Journal of Chemical Physics
|April 26, 2005
Summary
This study identifies three stable ONOOH conformers using advanced electronic structure theory, differing from prior research. Calculated properties like bond energies align with experimental data, providing valuable insights into ONOOH stability.
Area of Science:
- Computational Chemistry
- Theoretical Chemistry
- Quantum Chemistry
Background:
- Peroxynitrous acid (ONOOH) is an important molecule in atmospheric and biological chemistry.
- Previous theoretical studies have yielded conflicting results regarding the number and stability of ONOOH conformers.
- Accurate theoretical models are crucial for understanding ONOOH's properties and reactivity.
Purpose of the Study:
- To rigorously investigate the conformational landscape of ONOOH using high-level electronic structure theory.
- To determine the number and relative energies of ONOOH stationary points.
- To calculate key physical properties and thermodynamic data for ONOOH conformers.
Main Methods:
- High-level wave-function-based electronic structure theory (e.g., CCSD(T)) with augmented correlation-consistent basis sets.
- Density functional theory (DFT) using B-LYP and B3-LYP functionals.
- Multireference configuration interaction (MRCI) calculations for assessing multireference character.
- Isodesmic reaction schemes for calculating heats of formation and bond dissociation energies.
Main Results:
- Three ONOOH conformers (cis-cis, cis-perp, trans-perp) were identified as stationary point minima, contradicting some previous findings.
- Basis sets with diffuse functions are essential for accurate representation of the internal rotation potential energy surface.
- Calculated physical properties (geometries, dipole moments, vibrational frequencies) show good agreement with available experimental data.
- Peroxide bond dissociation energies for cis-cis and trans-perp conformers were computed as 19.3±0.4 and 16.0±0.4 kcal/mol, respectively, in agreement with gas-phase experiments.
Conclusions:
- The study confirms the existence of three stable ONOOH conformers, providing a reliable theoretical benchmark.
- CCSD(T)/aug-cc-pVTZ calculations offer accurate predictions for ONOOH properties where experimental data is lacking.
- The calculated thermodynamic data, including heats of formation and bond dissociation energies, enhance our understanding of ONOOH's stability and reactivity.