Searcharxiv⌕ Search
Home/Archive/arXiv

arXiv · 2610.23452

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

Miguel Jiménez-Redondo·Olli Sipilä·Petr Dohnal·Robin Dahl·Paola Caselli·Pavol Jusko
View original source ↗Read source document ↗Export metadata ↓

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 H$_2$ and CO, as well as three different reactions producing both isomers: CO$^+$ + H$_2$ , H$_3^+$ + CO, and ArH$^+$ + CO. Our results show that the reaction of CO$^+$ with H$_2$ 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.

Explore related subjects

astro-ph.GAphysics.chem-ph

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

Miguel Jiménez-Redondo, Olli Sipilä, Petr Dohnal, Robin Dahl, Paola Caselli, Pavol Jusko. 2026-10-16. Isomer-resolved ion-molecule reaction kinetics of HCO+ and HOC+. https://doi.org/10.1051/0004-6361%2F202663008

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related papers

arXiv2026

FRANZ: Framework for analytical one-zone blastwave dynamics

(abridged) We develop a flexible analytical framework for modeling blastwave evolution in arbitrary environments and use it to investigate how large-scale galactic structure affects the dynamics and morphology of evolved SNRs and SBs. We introduce FRANZ (FRamework for ANalytical one-Zone blastwave dynamics), a modular thin-shell model that follows the local evolution of a shock-surface segment in environments characterized by arbitrary density, velocity and gravitational fields. After validating the model against well-established analytical results, we apply it to study the effects of vertical stratification, galactic shear and dense galactic substructure on blastwave evolution. FRANZ reproduces the classical evolution of blastwaves in uniform media while extending to complex environments. We derive criteria for disk break out in stratified media, characterize the timescales on which differential rotation deforms blastwaves and identify a new mechanism, by which it can suppress the momentum coupling in continuously-driven blastwaves. Interactions with dense filaments modify both shock-surface morphology and dynamics and confound the interpretation of the expansion history of observed remnants, which depends on the density distribution prior to the onset of explosions, which is fundamentally inaccessible from the observed state. In highly structured media with a high volume-filling factor of diffuse gas, ages inferred from the observed state may be systematically overestimated. FRANZ provides a computationally inexpensive and extensible framework for studying blastwaves in realistic galactic environments. It offers a useful complement to numerical simulations for interpreting observations of evolved SNRs and SBs and for developing improved models of stellar feedback in large-scale simulations.

astro-ph.GA↗
arXiv2026

An ALMA study of hub-filament systems II.Quiescent filaments converging towards highly dynamic hubs

Hub-filament systems are networks of converging interstellar filaments, often with active star formation at their centres, that may play an important role in high-mass star formation. In the first paper of this series, we found that the mass fraction that ends up in a clump's most massive core is significantly higher in IR-dark hubs than in IR-bright clumps, suggesting that the most-massive cores form early on. Such early massive core formation requires large inflow rates and dynamically active IR-dark clumps. We now present N$_2$H$^+$(J=1-0) observations of six IR-dark hub-filament systems mapped with ALMA 12m, 7m, and total power at 3'' resolution, to trace the kinematics of the dense gas. The data show intricate emission structures and complex spectra. To characterise their kinematics, we have developed mwydyn, a fully-automated, multiple velocity component, hyperfine line-fitting code. Our results reveal that the emission invariably consists of quiescent individual filaments in the outskirts that converge towards the hub centres where a systematic increase in velocity dispersion and number of components is observed. We also find that the distribution of centroid velocities is remarkably similar between clumps, despite spanning more than one order of magnitude in mass. We propose that our results are best explained by the mixing of gravitationally-driven multi-directional inflows, resulting in highly complex and dynamic hub centres. We also discuss the implications of the observed differentiated filament and hub gas kinematics in the context of the 3D morphology of hub-filament systems.

astro-ph.GA↗
arXiv2026

HURACAN: A comparison of stellar and interstellar proper motions inside L1688

The assumption that molecular clouds are kinematically coupled to the young stellar populations forming within them is observationally still poorly constrained. With the transverse component $v_{\textrm{t}}$ of the interstellar medium (ISM) motion being largely unknown, the three-dimensional kinematic state of even the closest clouds remains incomplete. We provide the first direct measurement of the transverse motion of the ISM inside the Ophiuchus cloud L1688 and compare it with the kinematics of the surrounding young stellar populations. The measurement was obtained using intensity-based image registration applied to archival data, allowing us to generate a proper motion field of the studied regions and determine the cloud's bulk motion, $(μ_{α^*},μ_δ)^{\mathrm{ISM}}_{\mathrm{median}}=(-3.0, -24.1)$ mas yr$^{-1}$. This motion differs from the kinematics of the youngest population in Upper Scorpius by $3\pm1$ km s$^{-1}$, highlighting the possibility of a bias when using stars as a proxy for the ISM motion near star-forming regions. By comparing the cloud's motion with that of the youngest stellar population in the region and the B-star Oph S1 located within the cloud, we find that stellar feedback must have dynamically shaped the motion of the ISM over the last few million years. Furthermore, by studying a shell-like ISM structure appearing in L1688, we find evidence suggesting that this object is likely neither a typical Herbig-Haro object nor a supernova remnant, with its origin remaining a mystery. Our results demonstrate that archival and future high-resolution near-infrared observations can and will continue to enable measurements of ISM transverse motions in nearby clouds, opening a new window for studying ISM dynamics that is not accessible when using radial velocities alone.

astro-ph.GA↗