Metastable Peaks in the Mass Spectra of N2 and NO

Metastable ions dissociating by unimolecular transitions have been observed in the mass spectra of N2 and NO at (M / q)* = 7.00 and (M / q)* = 8.53, respectively. In N2 the transition of N2+ to N+ is shown to occur from a state with an A.P. of 24.9 ± 0.3 eV. The kinetic-energy release is 0.55 ± 0.10 eV; hence the dissociation is to the limit N+(3P) + N(4S0) at 24.30 eV. In NO the dissociation is to the limit O+(4S0) + N(4S0) at 20.101 eV. The observed A.P. and kinetic-energy release are 20.2 ± 0.2 and 0.04 ± 0.02 eV, respectively. Possible mechanisms of metastable dissociation by tunneling or predissociation are suggested.