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 Plus monthly

Global: Zendy Tools annual

Global: Zendy Tools monthly

Global: Zendy Free Plan

We present a new gas-grain chemical model for the combined isotopicfractionation of carbon and nitrogen in molecular clouds, in which the isotopechemistry of carbon and nitrogen is coupled with a time-dependent descriptionof spin-state chemistry. We updated the rate coefficients of some isotopicexchange reactions considered in the literature, and present here a set of newexchange reactions involving molecules substituted in $\rm ^{13}C$ and $\rm^{15}N$ simultaneously. We apply the model to a series of zero-dimensionalsimulations representing a set of physical conditions across a prototypicalprestellar core, exploring the deviations of the isotopic abundance ratios inthe various molecules from the elemental isotopic ratios as a function ofphysical conditions and time. We find that the $\rm ^{12}C/^{13}C$ ratio candeviate from the elemental ratio by up to a factor of several depending on themolecule, and that there are highly time-dependent variations in the ratios.The $\rm HCN/H^{13}CN$ ratio, for example, can obtain values of less than 10depending on the simulation time. The $\rm ^{14}N/^{15}N$ ratios tend to remainclose to the assumed elemental ratio within $\sim$ ten per cent, with no cleartrends as a function of the physical conditions. Abundance ratios between $\rm^{13}C$-containing molecules and $\rm ^{13}C$+$\rm ^{15}N$-containing moleculesshow somewhat increased levels of fractionation due to the newly includedexchange reactions, though still remaining within a few tens of per cent of theelemental $\rm ^{14}N/^{15}N$ ratio. Our results imply the existence ofgradients in isotopic abundance ratios across prestellar cores, suggesting thatdetailed simulations are required to interpret observations of isotopicallysubstituted molecules correctly, especially given that the various isotopicforms of a given molecule do not necessarily trace the same gas layers.

Combined model for $\rm ^{15}N$, $\rm ^{13}C$, and spin-state chemistry in molecular clouds