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Reaction Pathway Dynamics for Atmospheric Decomposition Reactions: Unimolecular Dissociation of H2COO
1Department of Chemistry, University of Basel, Klingelbergstrasse 80, CH-4056 Basel, Switzerland.
The Journal of Physical Chemistry Letters
|June 3, 2026
Summary
The smallest Criegee intermediate, H2COO, decomposes via direct and indirect pathways, influencing product energy distributions. This study reveals non-RRKM effects in fragmentation, highlighting the need for explicit molecular dynamics in atmospheric chemistry.
Area of Science:
- Atmospheric Chemistry
- Chemical Dynamics
- Computational Chemistry
Background:
- Understanding fragmentation branching ratios is crucial for atmospheric chemistry.
- The smallest Criegee intermediate (H2COO) plays a key role in atmospheric reactions.
Purpose of the Study:
- Investigate the molecular product channels and decomposition dynamics of H2COO.
- Analyze energy partitioning in fragmentation channels.
Main Methods:
- Utilized a high-quality, full-dimensional machine-learned potential energy surface (CASPT2/aug-cc-pVTZ).
- Analyzed translational, rotational, and vibrational energy distributions of fragmentation products.
- Investigated reaction pathways via explicit molecular dynamics.
Main Results:
- Identified two pathways for CO2 + H2 formation: a direct pathway with vibrationally excited CO2 and a pathway through formic acid.
- The indirect pathway allows H2 to populate excited vibrational levels (v > 0).
- Observed non-RRKM effects in fragmentation lifetimes, described by stretched exponentials (β = 0.9–1.3).
Conclusions:
- Decomposition dynamics of H2COO are complex, involving distinct pathways with different energy partitioning.
- Non-RRKM behavior necessitates explicit molecular dynamics simulations for accurate atmospheric modeling.
- Results provide molecular-level insights into atmospheric reaction mechanisms.
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