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Updated: Jun 14, 2025
12:11
Computation of Atmospheric Concentrations of Molecular Clusters from ab initio Thermochemistry
Published on: April 8, 2020
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Intracluster reaction dynamics of NO+(H2O)n
1Division of Applied Chemistry, Faculty of Engineering, Hokkaido University, Kita-ku, Sapporo 060-8628, Japan.
The Journal of Chemical Physics
|September 4, 2024
Summary
Nitric oxide (NO) and water clusters form nitrous acid (HONO) in the atmosphere. This study reveals intra-cluster reactions in ionized NO(H2O)n clusters are a key HONO formation pathway for n > 3.
Area of Science:
- Atmospheric Chemistry
- Physical Chemistry
- Computational Chemistry
Background:
- Nitric oxide (NO) and its water clusters are vital in the D-region atmosphere.
- Nitrous acid (HONO) is a precursor to hydroxyl radicals and secondary pollutants.
- Previous studies focused on sequential and bimolecular reactions, neglecting photo-reactions in neutral NO(H2O)n clusters.
Purpose of the Study:
- To investigate intra-cluster reactions in ionized NO(H2O)n clusters.
- To elucidate the formation mechanism of HONO from these clusters.
- To explore the role of cluster size and hydration energy.
Main Methods:
- Direct ab initio molecular dynamics simulations were employed.
- Investigated vertical ionization of neutral NO(H2O)n clusters.
- Analyzed intra-cluster reaction dynamics and product formation.
Main Results:
- For n > 3, ionized [NO+(H2O)n] clusters yield HONO and hydrated H3O+ via intra-cluster reactions.
- Reaction times for HONO formation were calculated to be approximately 150 fs for n = 4.
- Smaller clusters (n = 1-3) undergo solvent re-orientation without HONO formation.
Conclusions:
- Intra-cluster reactions in ionized NO(H2O)n clusters (n > 3) represent a significant HONO formation pathway.
- The hydration energy of H3O+ is crucial for promoting HONO formation, dependent on cluster size.
- This study highlights a previously overlooked mechanism for atmospheric HONO production.
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