Related Experiment Video
Updated: Jul 19, 2026
10:37
Spatial Separation of Molecular Conformers and Clusters
Published on: January 9, 2014
Dissociative recombination of cold H3+ and its interstellar implications
1Department of Chemistry, University of Illinois at Urbana-Champaign, 600 South Mathews Avenue, Urbana, IL 61801, USA. bjmccall@uiuc.edu
Summary
The abundant presence of trihydrogen cation (H3+) in diffuse interstellar clouds is puzzling. New experiments suggest this is likely due to a low electron fraction or high ionization rate, not a low dissociative recombination rate.
Area of Science:
- Astrochemistry
- Plasma Physics
- Quantum Chemistry
Background:
- Trihydrogen cation (H3+) is crucial for interstellar ion-molecule chemistry.
- Observed H3+ abundances in diffuse clouds exceed predictions from simple chemical models.
- The rate constant for dissociative recombination (DR) of H3+ with electrons is a key, yet controversial, parameter.
Purpose of the Study:
- To accurately determine the dissociative recombination rate constant for H3+ under conditions relevant to diffuse interstellar clouds.
- To resolve discrepancies in previous experimental measurements of the H3+ DR rate.
- To investigate the implications of the measured DR rate for H3+ abundance in diffuse interstellar clouds.
Main Methods:
- Performed dissociative recombination (DR) measurements of H3+ ions using the CRYRING ion storage ring.
- Utilized a supersonic expansion ion source to produce rotationally cold H3+ ions.
- Measured the DR rate constant at energies relevant to interstellar conditions.
Main Results:
- The measured DR rate constant for rotationally cold H3+ is not significantly lower than commonly assumed values.
- Experimental results suggest the high abundance of H3+ in diffuse clouds is not explained by a suppressed DR rate.
- The findings point towards alternative explanations for abundant H3+ in diffuse clouds.
Conclusions:
- The dissociative recombination rate constant of H3+ with electrons under interstellar conditions is likely close to previously assumed values.
- The large observed abundance of H3+ in diffuse interstellar clouds is probably caused by a low fractional abundance of electrons or an elevated ionization rate.
- Further research is needed to fully understand the chemical and physical conditions governing H3+ concentrations in diffuse interstellar clouds.
More Related Videos
Related Concept Videos
01:30Crossing Over
Crossing over is the exchange of genetic information between homologous chromosomes during prophase I of meiosis I. Genetic recombination gives rise to allelic diversity in the newly formed daughter cells. In humans, crossing over produces genetically distinct haploid egg and sperm cells that undergo fertilization to produce unique offspring. Before cell division starts, the germ cell’s chromosome(s) undergo duplication in the S phase of the cell cycle. As the cells enter prophase I, duplicated...
01:16Thermal Sigmatropic Reactions: Overview
Sigmatropic rearrangements are a class of pericyclic reactions in which a σ bond migrates from one part of a π system to another. These are intramolecular rearrangements where the total number of σ and π bonds remain unchanged.
Sigmatropic shifts are classified based on an order term [i, j ], where i and j indicate the number of atoms across which each end of the σ bond migrates. Below are examples of a [3,3] sigmatropic shift in 1,5-hexadiene, referred to as...
Sigmatropic shifts are classified based on an order term [i, j ], where i and j indicate the number of atoms across which each end of the σ bond migrates. Below are examples of a [3,3] sigmatropic shift in 1,5-hexadiene, referred to as...
01:04¹³C NMR: ¹H–¹³C Decoupling
The probability of having two carbon-13 atoms next to each other is negligible because of the low natural abundance of carbon-13. Consequently, peak splitting due to carbon-carbon spin-spin coupling is not observed in spectra. However, protons up to three sigma bonds away split the carbon signal according to the n+1 rule, resulting in complicated spectra.
A broadband decoupling technique is used to simplify these complex, sometimes overlapping, signals. Broadband decoupling relies on a...
A broadband decoupling technique is used to simplify these complex, sometimes overlapping, signals. Broadband decoupling relies on a...
00:54Radical Formation: Homolysis
A bond is formed between two atoms by sharing two electrons. When this bond is broken by supplying sufficient energy, either two electrons can be taken up by one atom forming ions by the cleavage called heterolysis, or the two electrons are shared by two atoms, with one each creating radicals by the cleavage called homolysis.
03:40Hess's Law
There are two ways to determine the amount of heat involved in a chemical change: measure it experimentally, or calculate it from other experimentally determined enthalpy changes. Some reactions are difficult, if not impossible, to investigate and make accurate measurements for experimentally. And even when a reaction is not hard to perform or measure, it is convenient to be able to determine the heat involved in a reaction without having to perform an experiment.
02:53Conservative Site-specific Recombination and Phase Variation
Because the DNA segments are cut and reorganized in a direction-specific manner, site-specific recombination has emerged as an efficient genetic engineering technique. Flippase and Cyclization recombinases or Flp and Cre, respectively, are two members of the tyrosine recombinase family derived from bacteriophages, that are used to mediate site-specific DNA insertions, deletions, and targeted expression of proteins in mammalian cell lines.
The recognition sites for Cre recombinase called LoxP...
The recognition sites for Cre recombinase called LoxP...