The Remarkable I₂O₃ Molecule: A New View from Theory.

Area of Science:

• Atmospheric chemistry
• Computational chemistry
• Chemical physics

Background:

• Atmospheric iodine chemistry is increasingly important due to rising iodine emissions.
• Iodine oxides (I2O3-5) are critical precursors for atmospheric particle formation.
• Iodine trioxide (I2O3) is the simplest iodine oxide involved in particle formation but remains atmospherically undetected.

Purpose of the Study:

• To provide accurate theoretical characterizations of iodine trioxide (I2O3) using high-level computational methods.
• To investigate the potential energy surface of I2O3 and discover new isomers.
• To assess the performance of various computational methods and DFT functionals for atmospheric chemistry applications.

Main Methods:

• Geometries of I2O3 were optimized using the CCSD(T)/aug-cc-pwCVTZ-PP level of theory.
• Harmonic vibrational frequencies were computed at the CCSD(T)/aug-cc-pwCVTZ-PP level.
• High-level CCSDT(Q) calculations with extrapolation to the Complete Basis Set (CBS) limit were performed for accurate energetics.

Main Results:

• The study presents the first geometries optimized exclusively with coupled-cluster theory (CCSD(T)).
• New isomers of I2O3 were identified on its potential energy surface.
• Accurate I2O3 energetics were obtained, including zero-point vibrational and scalar relativistic corrections.

Conclusions:

• This work provides a robust theoretical foundation for understanding I2O3.
• The discovery of new isomers expands the known chemistry of iodine oxides.
• The assessment of computational methods offers guidance for future atmospheric chemistry studies.