The lithium clusters Li2, Li4, and Li8 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 Li4 cluster possesses a rhombic structure (D2h) with calculated d(Li–Li)=272.6 and 306.4 pm, respectively. For octalithium, a hypertetrahedral structure (Td) 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.

Bromine oxides have been generated by passing a mixture of Br(2)/O(2)/Ar through a microwave discharge. The products were stabilized at 6.5 K in an excess amount of argon. Infrared spectroscopy was used to analyze the species formed; experiments with enriched (18)O(2) and ab initio calculations were carried out to assist in the assignment of the spectra. Besides the known species BrO, OBrO, and BrBrO, spectroscopic evidence for BrOBrO, BrBrO(2), and a new isomer of Br(2)O(3) is reported for the first time. Extensive comparisons are drawn between the present studies and previous experimental and theoretical works. The chemistry involved in the production of the observed compounds is discussed. The assignments are corroborated by the good correlation between observed and calculated band positions and intensities.

The sodium molecules Na(2), Na(4), and Na(8) have been isolated in argon matrixes at 15 K and characterized for the first time by Raman spectroscopy. The vibrational frequencies are compared with density functional (DFT) calculations. The Na(4) cluster possesses a rhombic structure (D(2h)) with calculated d(Na-Na) = 307.2 and 347.4 pm, respectively. For octasodium, a hypertetrahedral structure (T(d)) is predicted in which each side of an inner tetrahedron with d(Na-Na) = 331.5 pm is capped by sodium atoms with a distance of d(Na-Na) = 348.7 pm. The green octasodium cluster is the first example of a matrix-isolated magic number cluster. Its formation from blue tetrasodium is discussed on the basis of the observed sequence of cluster growth.

The magnesium molecules Mg(2), Mg(3), Mg(4), and Mg(5) have been isolated in rare-gas matrixes at 8 K and characterized for the first time by Raman spectroscopy. The vibrational frequencies were compared with those obtained by density functional theory calculations. The fundamental frequency of the dimer was observed at 97 cm(-1) (Ar matrix), and a bond length of d(Mg-Mg) = 340.8 pm was calculated. The Mg(3) cluster possesses a triangular structure (D(3h)) with calculated d(Mg-Mg) = 317.8 pm. For tetramagnesium, a tetrahedral structure (T(d)) with d(Mg-Mg) = 301.3 pm is predicted. The Mg(5) molecule possesses a trigonal-bipyramidal structure (D(3h)) with d(Mg-Mg) = 293.1 and 322.5 pm, respectively. The red tetramagnesium cluster is an example of a matrix-isolated magic number cluster.