Determine the contribution of HNC to cometary m/z 27 signal

Determine whether, and in what abundance, hydrogen isocyanide (HNC) contributes to the m/z 27 signal measured in comet 67P/Churyumov-Gerasimenko by Rosetta’s ROSINA Double Focusing Mass Spectrometer, given the inability of the available data to distinguish HNC from hydrogen cyanide (HCN).

Background

The paper explains that HCN and HNC are structural isomers with the same nominal mass and that the DFMS measurements cannot unambiguously separate their contributions. HCN is identified through its molecular-ion and hydrogen-loss signals, but no electron-ionization mass-spectrum reference data are available for HNC. Both species have been reported in cometary observations, and their relative abundance appears to vary with cometocentric and heliocentric distance, suggesting that the unresolved contribution of HNC is relevant to interpreting cometary nitrogen chemistry and possible interstellar inheritance.

References

But the DFMS data is compatible with the fragmentation pattern of HCN, and it is unclear if and how much HNC contributes.

— Nitrogen- and nitrogen-oxygen-bearing organic molecules in comet 67P/Churyumov-Gerasimenko: An untargeted investigation  (2608.24235 - Hänni et al., 25 Aug 2026) in Table 1 footnote (c); Section 3, subsection “C_nH_mN species,” discussion of HCN