Low-lying quartet electronic states of nitrogen dioxide

Area of Science:

• Computational Chemistry
• Molecular Physics
• Quantum Chemistry

Background:

• Nitrogen dioxide (NO2) is an environmentally significant molecule.
• Understanding its electronic states is crucial for atmospheric and chemical research.

Purpose of the Study:

• To systematically investigate the electronic ground and low-lying quartet states of NO2.
• To determine excitation energies and molecular geometries of these states using high-level theoretical methods.

Main Methods:

• Employed various high-level theoretical methods including SCF, CASSCF, CISD, CCSD, CCSD(T), and ICMRCI.
• Utilized Dunning's correlation consistent polarized valence and augmented basis sets (cc-pVXZ, aug-cc-pVXZ where X=T,Q,5).
• Calculated adiabatic excitation energies (Te) and quantum mechanical excitation energies (T0) for quartet states.

Main Results:

• Predicted excitation energies for the ã 4A2, b 4B2, and c 4A1 quartet states.
• Determined bond angles for the Renner-Teller 4Pi state leading to a 4A2 and b 4B2 states.
• Observed peculiar behavior in the b 4B2 state regarding its equilibrium geometry (Cs vs. C2v), highlighting the importance of correlation treatments.

Conclusions:

• The study provides accurate theoretical predictions for NO2's electronic states.
• The findings offer insights into the complex electronic structure and geometry of NO2, particularly the b 4B2 state.
• Emphasizes the critical role of dynamical and nondynamical correlation in accurately describing molecular properties.