Do nitrogen-atom-containing endohedral fullerenes undergo the shrink-wrap mechanism?

The endohedral nitrogen-atom-containing fullerenes, N@C-60 and N@C-70, were studied mass spectrometrically. The neutral endohedrals are thermally unst able. This instability can be followed by mass spectrometry as well as by E PR spectroscopy. The corresponding ions were studied by using mass-analyzed ion kinetic energy (MIKE) spectroscopy. Unlike metal-containing and noble- gas-containing endohedral fullerenes studied earlier, the ions N@C-60(+) an d N@C-70(+) do not lose C-2 groups unimolecularly but lose the nitrogen ato m instead. This indicates that the activation energy for nitrogen-atom loss is lower than that for the C-2 elimination from the cage. This was verifie d through the analysis of kinetic energy release distribution (KERD) measur ements. The results are discussed in light of the thermal instability of ni trogen-atom-containing endohedral compounds compared to noble-gas-containin g analogues.