On the basis of semiempirical and high-level ab initio calculations, t
heoretical evidence is presented of a ''window'' mechanism operable on
the surface of C60 and other fullerenes. Through this mechanism, larg
e holes may be formed in fullerenes excited to their triplet state, op
enings through which atoms and small molecules can pass. This work pro
vides a theoretical foundation for experiments that have prepared endo
hedral noble gas compounds of C60 under thermal excitation. A method i
s proposed that could increase the efficiency of the process of noble
gas insertion into C60 and provide a more general means to create endo
hedral fullerene compounds.