English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

The $\mathrm{H}_2$ formation on grains is known to be sensitive to dusttemperature, which is also known to fluctuate for small grain sizes due tophoton absorption. We aim at exploring the consequences of simultaneousfluctuations of the dust temperature and the adsorbed H-atom population on the$\mathrm{H}_2$ formation rate under the full range of astrophysically relevantUV intensities and gas conditions. The master equation approach is generalizedto coupled fluctuations in both the grain's temperature and its surfacepopulation and solved numerically. The resolution can be simplified in the caseof the Eley-Rideal mechanism, allowing a fast computation. For theLangmuir-Hinshelwood mechanism, it remains computationally expensive, andaccurate approximations are constructed. We find the Langmuir-Hinshelwoodmechanism to become an efficient formation mechanism in unshielded photondominated region (PDR) edge conditions when taking those fluctuations intoaccount, despite hot average dust temperatures. It reaches an importancecomparable to the Eley-Rideal mechanism. However, we show that a simpler rateequation treatment gives qualitatively correct observable results in full cloudsimulations under most astrophysically relevant conditions. Typical differencesare a factor of 2-3 on the intensities of the $\mathrm{H}_2$ $v=0$ lines. Wealso find that rare fluctuations in cloud cores are sufficient to significantlyreduce the formation efficiency. Our detailed analysis confirms that the usualapproximations used in numerical models are adequate when interpretingobservations, but a more sophisticated statistical analysis is required if oneis interested in the details of surface processes.

Surface chemistry in the Interstellar Medium II. $\mathrm{H}_2$ formation on dust with random temperature fluctuations