Structure and relative energies of some nitrogen-containing radical cations by MNDO calculation

MNDO calculations have been performed on the energy surfaces of four nitrogen-containing radical cations: [CH3N]˙+, [CH5N]˙+, [N2H4]˙+, and [N2H2]˙+. In general, the calculated structures and relative energies compare well with ab initio calculations and experiment (when available). The MNDO method overestimates the stabilities of non-classical isomers and consequently underestimates the energy barriers of 1,2-hydrogen shifts connecting both classical and non-classical species. The energy barriers for the loss of H atoms from X atoms (H–X–N–) are overestimated while those from N atoms (–X–N–H) are underestimated. Specific fragmentations or isomerization within each radical cation are also commented on. The results on the whole suggest that MNDO is a suitable method in this area.