The hydrogenation of the aza[60]fullerene C59N. has been studied in situ. The C59N. monomer is formed by thermal evaporation and dissociation of the (C59N)(2) dimer and is hydrogenated in the heated inlet channel of a mass spectrometer, which is used subsequently for the product analysis. In addition to the expected formation of C59NH, the abundant production of C59NH5 is observed. Increasing the availability of hydrogen for the reduction enhances the formation of C59NH5, which is eventually obtained as the main product. The effective yield curves of the negative ions C59NHx-, where x = 0, 1 and 5 are detailed and contrasted with the ion yields of C60Hx-, where x = 0, 2 and 6. It is found that increasing hydrogen attainment reduces the energy range in which long-lived molecular ions can result from electron capture. (C) 2002 Elsevier Science B.V. All rights reserved.