Coevaporation of C60 and an alkali metal in a gas aggregation cell yie
lds a distribution of clusters with composition (C60)nMx with 0 less-t
han-or-equal-to x < 150, n = 1,2,3, and M = Li, Na, and K. For singly
ionized clusters the mass peaks are strong for odd values of x but onl
y after reaching the composition C60M7+. It is suggested that the onse
t of even-odd alternation marks the end of electron transfer between m
etal and C60 and the beginning of metal-metal bonding.