The unimolecular chemistry of protonated hydroxylamine

The unimolecular chemistry of protonated hydroxylamine has been investigate d using mass spectrometric and ab initio methods. Calculation of the proton affinity shows that the nitrogen atom is the most basic site. There is an activation barrier of 211 kJ mol(-1) for the isomerization to the structure corresponding to protonation on oxygen. Thorough studies of the potential energy surface by ab initio methods correlate well with the observed peaks in the mass-analyzed ion kinetic energy (MIKE) spectrum. N-15 labelling has been used to identify fragmentation products unambiguously. In contrast to several isoelectronic systems, loss of H-2 is not a major process in the M IKE-spectrum. The importance of spin change, as has recently been seen for other protonated systems, becomes evident in this study. The theoretical ca lculations show that the main process, loss of NH, can only be explained by a cross-over from the singlet to the triplet surface. (Int J Mass Spectrom 185/186/187 (1999) 231-240) (C) 1999 Elsevier Science B.V.