Explain the unexplained C_mH_nNO signal at m/z 55

Determine which C₂HNO parent species accounts for the clearly underpopulated m/z 55 signal in the ROSINA DFMS spectrum of comet 67P/Churyumov-Gerasimenko, including whether the signal arises from cyanoformaldehyde, iminoethenone, nitrosoacetylene, ketoaziridine, oxoacetonitrile, or another structural isomer.

Background

The spectral deconvolution leaves a substantial unexplained signal at m/z 55 corresponding to the C₂HNO sum formula. The authors infer that an additional parent molecule producing a molecular-ion signal but not a molecular-ion-minus-hydrogen signal may be required. Several chemically plausible structures are listed, but none can be evaluated decisively because electron-ionization reference spectra are unavailable. This unresolved assignment limits the completeness of the inventory of nitrogen-oxygen-bearing cometary organics.

References

The reason for the peak in signal intensity for C_mH_nNO species where m = 4, however, is unclear.

— Nitrogen- and nitrogen-oxygen-bearing organic molecules in comet 67P/Churyumov-Gerasimenko: An untargeted investigation  (2608.24235 - Hänni et al., 25 Aug 2026) in Section 4.1, “Unexplained intensity”