The lithium clusters Li-2, Li-4, and Li-8 have been isolated in argon matrices at 15 K and characterized by Raman spectroscopy. The vibrational frequencies are compared with configuration interaction (QCISD/6-311G* and CID/6-311G*) calculations and their assignment is supported by 6-lithium and 7-lithium isotopomers. The Li-4 cluster possesses a rhombic structure (D-2h) with calculated d(Li-Li)=272.6 and 306.4 pm, respectively. For octalithium, a hypertetrahedral structure (T-d) is predicted in which each side of an inner tetrahedron with d(Li-Li)=292.5 pm is capped by lithium atoms with a distance of d(Li-Li)=304.2 pm. The octalithium cluster is an example of a matrix-isolated magic number cluster. (C) 2003 American Institute of Physics.