Isomer-resolved ion-molecule reaction kinetics of HCO+ and HOC+

The HCO + /HOC + abundance ratio has been observed to vary significantly in different astrophysical environments, making it an important diagnostic tool for exploring the interstellar medium.

By Jiménez-Redondo, Sipilä, Dohnal +3Oct 16, 2026

Score████░░░░░░4.1

VerdictWorth a reader's time today.

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Abstract

The HCO⁺/HOC⁺ abundance ratio has been observed to vary significantly in different astrophysical environments, making it an important diagnostic tool for exploring the interstellar medium. However, uncertainties in the reaction rates and branching ratios of key chemical reactions involving these ions affect the conclusions drawn from observations of either these species or other species that are derived on their basis. Here, we present isomer-resolved ion-molecule reaction rate coefficients of reactions involving HCO⁺ and HOC⁺ using a cryogenic ion trap experiment. We measured the rate coefficients of the isomerization reaction of HOC⁺ to HCO⁺ with H₂ and CO, as well as three different reactions producing both isomers: CO⁺ + H₂, H₃⁺ + CO, and ArH⁺ + CO. Our results show that the reaction of CO⁺ with H₂ predominantly produces HCO⁺ with a negligible yield of HOC⁺ . This result is in agreement with recent theoretical predictions, but in major contrast to the generally accepted branching ratio based on previous experimental results. We also find that the isomerization reaction of HOC⁺ to HCO⁺ is efficient with both H2 and CO. We were able to assess the impact of our new measured reaction rate coefficients on the predicted HCO⁺/HOC⁺ abundance ratio using a state-of-the-art astrochemical model.

Miguel Jiménez-Redondo, Olli Sipilä, Petr Dohnal, Robin Dahl, Paola Caselli, Pavol Jusko

The editor's rubric

Heuristic review

Leverage3 / 5: A method or resource many groups across the field will adopt within a year.; 18% of this desk’s rubric
Magnitude3 / 5: Large gain: roughly 2x, or a clear new state of the art on a hard, unsaturated problem.; 20% of this desk’s rubric
Evidence3 / 5: Solid: multiple benchmarks or cohorts, ablations, fair baselines, released code or data.; 22% of this desk’s rubric
Novelty2 / 5: A new combination of known ideas.; 22% of this desk’s rubric
Trajectory2 / 5: Some room to improve with obvious engineering.; 10% of this desk’s rubric
Stakes2 / 5: Benefits a professional community (practitioners, clinicians, engineers).; 8% of this desk’s rubric

Dimension	Level	Weight	What that level means
Leverage	███░░ 3	18%	A method or resource many groups across the field will adopt within a year.
Magnitude	███░░ 3	20%	Large gain: roughly 2x, or a clear new state of the art on a hard, unsaturated problem.
Evidence	███░░ 3	22%	Solid: multiple benchmarks or cohorts, ablations, fair baselines, released code or data.
Novelty	██░░░ 2	22%	A new combination of known ideas.
Trajectory	██░░░ 2	10%	Some room to improve with obvious engineering.
Stakes	██░░░ 2	8%	Benefits a professional community (practitioners, clinicians, engineers).

Editor’s rationale

Heuristic triage from title and abstract text only, not a reading of the paper. Cues found: method (we propose); gains (state of the art); verification (error bars); scale (efficient). Red flags: derivative (modified version).

How the score was computed

rank-2026-10-18

Score████░░░░░░4.1

Score = 10 × (75% × adjusted merit / 10 + 15% × attention + 10% × freshness)

Desks place stronger verdicts first, then use this score to order work within the same verdict.

Merit: 5.2 / 10; Weighted rubric, evidence-gated.
Adjusted merit: 4.5 / 10; Shrunk toward the desk prior by editor confidence (38%).
Attention: 0%; Citations, upvotes, points, mentions.
Freshness: 76%; Half-life decay since publication.

No attention signals recorded yet.

The record

Reviewed by heuristic-v7 on Oct 19, 2026, 07:29 UTC. Paper type: method.
Categories: astro-ph.GA, physics.chem-ph
BRIEF, No.6 in the Physics edition of October 19, 2026.