STUDIES OF METALLOFULLERENE PRIMARY SOOTS BY LASER AND THERMAL-DESORPTION MASS-SPECTROMETRY

Laser desorption (LD) and thermal desorption (TD) mass spectra of the metallofullerenes found in arc-produced primary soots have been studie d for a large variety of alkaline earth and lanthanide elements. The m etallofullerene ratios found in the LD spectra indicate that two disti nct groups are observed: Sc, Y, La, Ce, Pr, Nd, Gd, Tb, Ho, Er, and Lu (group A) and Ca, Sr, Sm, Eu, and Yb (group B). The TD spectra of mos t of these same soots also separate into two groups that contain the s ame elements as groups A and B. Group A metallofullerenes show strong signals in both LD and TD spectra. Group B metallofullerenes are disti nguished by their presence in the LD spectra but absence in the TD spe ctra. From the general ionic behavior of the elements of these groups, and recent studies of the endohedral oxidation states, we propose tha t the oxidation states are +3 for group A and +2 for group B. C70 meta llofullerenes are anomalous in that they are absent in TD spectra for all group A and B elements, even at T = 750-degrees-C, but present in LD spectra.