The unimolecular decomposition rates of energy selected methylnitrite and deuterated methylnitrite ions

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Abstract
The fragmentation of methylnitrite ion (CH3ONO+) involves dissociation from noninterconverting electronic states characterized by the formation of CH3O+ (m/z=31) and NO+ (m/z=30) ions. The lifetimes of the precursors of these ions have been determined from ion time‐of‐flight curves obtained by threshold photoelectron–photoion coincidence (TPEPICO) mass spectrometry. The deuterated methylnitrite ion (CD3ONO+) was also studied to examine the kinetic isotope effects on ion lifetimes. The rate constants for the reactions leading to the formation of CH3O+ and CD3O+ were found to be independent of internal energy over ∼0.2 and 0.9 eV, respectively. The isotope effect increases with increasing internal energy, contrary to that expected from the quasiequilibrium theory (QET) of mass spectra. We suggest that methylnitrite ion fragmenting to CH3O+ and NO+ occurs from noncompeting noninterconverting electronic states involving a surface crossing.