Metastable peaks have been observed from the unimolecular decomposition of an excited intermediate ion formed by ion-molecule reaction in a high-pressure chemical ionization source. Chemical ionization of methanol with H3+ was used to produce excited protonated methanol ions, m/e = 33, for which metastables were observed for decomposition to protonated formaldehyde (m/e = 31) and methyl cations (m/e = 15):
The metastable peak for 33 → 31 is broad and Xshed-topped, and yields a kinetic-energy release of 0.93 eV. The shape of the metastable for 33 → 15 is Gaussian and narrow, corresponding to an energy release of only 0.002 eV.