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1Clear out junk files and repair common Windows errors2Scan for outdated or missing drivers - takes under a minute3Repair Windows errors before they cause bigger problemsA 2011 experiment measured how quickly atomic nitrogen reacts with hydroxyl radicals at low temperatures. Its result helps scientists evaluate one proposed gas-phase pathway to molecular nitrogen in interstellar clouds—but it did not measure the amount of nitrogen in any cloud.
What reaction did the experiment measure?
Julien Daranlot and colleagues studied the barrierless reaction N(⁴S) + OH(²Π) → H(²S) + NO(²Π). In this reaction, atomic nitrogen and the hydroxyl radical produce nitric oxide (NO) and a hydrogen atom. The team’s study, “Revealing atom-radical reactivity at low temperature through the N + OH reaction,” appeared in Science on 16 December 2011. The PubMed record describes the kinetic measurements and reports agreement with exact and approximate quantum-mechanical calculations.
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How did researchers measure the reaction?
The team used a supersonic-flow reactor with a Laval nozzle to create a cold, rapidly flowing gas. Microwave discharge generated atomic nitrogen, and the researchers followed the reaction kinetics using a relative-rate method: they inferred the target reaction’s rate by comparing its progress with that of a reference reaction under the experimental conditions.
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Clear out junk files and repair common Windows errorsFree Scan →Fix the driver behind crashes, sound loss and screen glitchesFind Drivers →Repair Windows errors before they cause bigger problemsFix Now →A 2012 NOAA conference presentation provides broader context for this experimental approach, describing CRESU supersonic flow, microwave discharge, pulsed laser photolysis with laser-induced fluorescence, and relative-rate analysis. Its materials summarize N + OH and N + CN studies across 56–296 K; that range describes the presentation’s coverage, not the temperature range of the 2011 N + OH result alone. NOAA Chemical Sciences Laboratory conference materials
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What did the low-temperature result show?
The lowest temperature reported for the 2011 measurement was 56 K, according to Chemistry World’s contemporaneous account. That report says the measured rates were lower than previous measurements. The PubMed abstract confirms that the observed rates agreed with exact and approximate quantum calculations, but it does not state a numerical rate constant; a specific value should not be inferred from the abstract.
The temperature matters because dense interstellar clouds are colder still. Chemistry World’s 2011 report cites approximately 10 K as more representative of those environments. The laboratory measurement therefore probed cold chemistry, but it did not reproduce the clouds’ temperature exactly.
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How does N + OH connect to molecular nitrogen?
The measured reaction makes NO, not molecular nitrogen (N₂). In the proposed sequence, that NO can react with an excess nitrogen atom:
- N + OH → H + NO: the reaction measured in the laboratory supplies NO.
- N + NO → N₂ + O: a subsequent reaction can convert NO into molecular nitrogen.
Measuring the first reaction’s rate helps modelers assess how efficiently this proposed route can supply NO for the next step. Combined with other chemical processes and conditions, that information can change predictions of gas-phase N₂ formation. It cannot, by itself, establish a cloud’s N₂ abundance or prove that this pathway dominates there. The study’s abstract describes the result as insight into gas-phase mechanisms for forming molecular nitrogen in interstellar clouds.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.What the experiment can—and cannot—tell us
| Evidence | What it supports | What it does not establish |
|---|---|---|
| Laboratory kinetics for N + OH, measured down to 56 K (Chemistry World, 2011) | The reaction rate under the reactor’s experimental conditions | The abundance of N₂ in a particular cloud |
| Agreement with exact and approximate quantum calculations (Daranlot et al., 2011) | Consistency between measured rates and those calculations | That the laboratory gas exactly reproduces interstellar conditions |
| A proposed follow-on reaction, N + NO → N₂ + O (Chemistry World, 2011) | A possible link from NO production to molecular nitrogen formation | That this is the only, or dominant, route to N₂ in clouds |
The central contribution is thus a more informative rate for a reaction used in astrochemical models. The result refines an input to those models; determining what a specific cloud contains requires evidence beyond this single laboratory reaction measurement.
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