X-ray induced fragmentation of fulminic acid, HCNO

The fragmentation of fulminic acid, HCNO, after excitation and ionization of core electrons was investigated using Auger-electron–photoion coincidence spectroscopy. A considerable degree of site-selectivity is observed. Ionization of the carbon and oxygen 1s electron leads to around 70% CH⁺ + NO⁺, while ionization at the central N-atom produces only 37% CH⁺ + NO⁺, but preferentially forms O⁺ + HCN⁺ and O⁺ + CN⁺. The mass-selected Auger-electron spectra show that these fragments are associated with higher binding energy final states. Furthermore, ionization of the C 1s electron leads to a higher propensity for C–H bond fission compared to O 1s ionization. Following resonant Auger–Meitner decay after 1s → 3π excitation, 12 different ionic products are formed. At the C 1s edge, the parent ion HCNO⁺ is significantly more stable compared to the other two edges, which we also attribute to the higher contribution of final states with low binding energies in the C 1s resonant Auger electron spectra.