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Updated: Jan 16, 2026
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Reaction Kinetics and Combustion Dynamics of I4O9 and Aluminum Mixtures
Published on: November 7, 2016
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Ionic Reactant Orientation Inhibits Ion-Neutral Reactions at Low Temperatures
Yongxu Peng1, Junlong Li2, Zongao Song1
1State Key Laboratory of Quantum Functional Materials, Department of Chemistry, and Center for Advanced Light Source, Southern University of Science and Technology, Shenzhen, Guangdong 518055, China.
JACS Au
|September 26, 2025
Summary
Barrierless ion-molecule reactions in interstellar chemistry are slower than predicted. Steric effects, or molecular orientation, significantly impact reaction rates at low temperatures, requiring improved models.
Area of Science:
- Astrochemistry
- Chemical Physics
- Quantum Chemistry
Background:
- Barrierless ion-molecule reactions are crucial for interstellar chemistry, especially at low temperatures.
- Classical capture theory often overestimates reaction rates by neglecting ion orientation.
Purpose of the Study:
- To investigate the rate coefficient of the BeD+ and O2 reaction at low temperatures.
- To determine the influence of steric effects on ion-molecule reaction dynamics.
Main Methods:
- Utilized a linear quadrupole ion trap and time-of-flight mass spectrometry.
- Employed sympathetically cooled BeD+ ions and O2.
- Performed isotopic substitution to confirm reaction products.
- Conducted master equation modeling with high-level electronic structure calculations (CCSDT-(Q)).
Main Results:
- Measured rate coefficient k = (5.4 ± 1.2) × 10^-11 cm^3/s at 97 K.
- Observed rate is ~15 times lower than predicted by classical capture theory.
- Identified BeOD+ and O as the sole products.
- Master equation modeling accurately reproduced experimental results.
Conclusions:
- Steric constraints significantly reduce reactivity in barrierless ion-molecule reactions at low temperatures.
- Classical capture theory overestimates reaction rates due to its neglect of steric effects.
- Accurate interstellar chemistry models must incorporate steric considerations for ion-molecule reactions.
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