Low-energy fragmentations of five isomeric [H3, C,N, O2] +· ions

The low-energy fragmentation characteristics of the H₃,C,N,O₂]^+· isomers H₃CNO₂]^+· (a), H₂C?N(O)OH]^+· (b), H₃CONO]^+· (c), HC(O)NHOH]^+· (d) and HC(OH)?NOH]^+· (e) were studied in detail by metastable ion mass spectrometry. In agreement with most earlier observations, appearance energy measurements established the potential energy surface of the isomers a, b and c, showing the intricate interrelations between them. It was concluded that a isomerizes into b prior to fragmentation by loss of ^·OH and H₂O and into c before loss of ^·H and H₃CO^· moreover, the reverse reactions do not take place on the metastable time-frame. The dominant metastable process for isomers d and e (obtained via HCN loss from glyoxime) was generation of H₂NOH]^+·. For isomer e this process was proposed to involved a rate-determining isomerization into d. It was concluded that isomers d and e do not intercommunicate with ions a, b and c prior to fragmentation. Neutralization-reionization mass spectrometry indicated that the enol form of formohydroxamic acid as well as the keto counterpart are stable in the gas phase.