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 unidentified infrared emission (UIE) features at 3.3, 6.2, 7.7, 8.6, and11.3 micrometer, commonly attributed to polycyclic aromatic hydrocarbon (PAH)molecules, have been recently ascribed to mixed aromatic/aliphatic organicnanoparticles. More recently, an upper limit of <9% on the aliphatic fraction(i.e., the fraction of carbon atoms in aliphatic form) of the UIE carriersbased on the observed intensities of the 3.4 and 3.3 micrometer emissionfeatures by attributing them to aliphatic and aromatic C-H stretching modes,respectively, and assuming A_34./A_3.3~0.68 derived from a small set ofaliphatic and aromatic compounds, where A_3.4 and A_3.3 are respectively theband strengths of the 3.4 micrometer aliphatic and 3.3 micrometer aromatic C-Hbonds.  To improve the estimate of the aliphatic fraction of the UIE carriers, herewe analyze 35 UIE sources which exhibit both the 3.3 and 3.4 micrometer C-Hfeatures and determine I_3.4/I_3.3, the ratio of the power emitted from the 3.4micrometer feature to that from the 3.3 micrometer feature. We derive themedian ratio to be <I_3.4/I_3.3> ~ 0.12. We employ density functional theoryand second-order perturbation theory to compute A_3.4/A_3.3 for a range ofmethyl-substituted PAHs. The resulting A_3.4/A_3.3 ratio well exceeds 1.4, withan average ratio of <A_3.4/A_3.3> ~1.76. By attributing the 3.4 micrometerfeature exclusively to aliphatic C-H stretch (i.e., neglecting anharmonicityand superhydrogenation), we derive the fraction of C atoms in aliphatic form tobe ~2%. We therefore conclude that the UIE emitters are predominantly aromatic.

astrophysical journal/the astrophysical journal

The Carriers of the Interstellar Unidentified Infrared Emission  Features: Constraints from the Interstellar C-H Stretching Features at  3.2-3.5 Micrometers