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Conical Intersection Governs Ultrafast Photodissociation Dynamics of HO2NO2
1School of Emergency Management and Safety Engineering, China University of Mining and Technology-Beijing, Beijing 100083, P.R. China.
ACS Omega
|August 14, 2026
Summary
Peroxynitric acid (HO2NO2) photodissociation primarily yields NO2 and HO2 fragments. This study reveals ultrafast S1->S0 relaxation and a dominant dissociation pathway, driven by excited-state geometry.
Area of Science:
- Atmospheric Chemistry
- Quantum Chemistry
- Photochemistry
Background:
- Peroxynitric acid (HO2NO2) is a key atmospheric compound.
- Understanding its photodissociation is crucial for atmospheric modeling.
Purpose of the Study:
- Investigate the ultraviolet photodissociation dynamics of HO2NO2.
- Elucidate the mechanisms governing its dominant reaction pathways.
Main Methods:
- Complete active space SCF electronic structure calculations.
- Nonadiabatic molecular dynamics using fewest-switches surface hopping.
- Characterization of minimum-energy crossing points.
Main Results:
- Identified sloped single-path S0/S1 and peaked bifurcating T1/T2 crossings.
- Simulations show ultrafast S1 -> S0 relaxation and dominant NO2 + HO2 channel.
- Predicted pathway aligns with experimental photolysis data.
Conclusions:
- Excited-state molecular geometry dictates HO2NO2 photodissociation behavior.
- Structural origins of the dominant NO2 + HO2 pathway elucidated.
- Results improve atmospheric models and understanding of HO2NO2 photochemistry.
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