The rubidium molecules Rb(2) and Rb(3) and the cesium molecules Cs(2) and Cs(3) were isolated in argon matrixes and characterized for the first time by Raman spectroscopy. The fundamental frequencies of the dimers were observed at 59.1 cm(-)(1) for the rubidium dimer and 45.8 cm(-)(1) for the cesium dimer. The Raman lines of the rubidium trimer appeared at 38.3 and 53.9 cm(-)(1), and the lines of the cesium trimer, at 24.4 and 39.5 cm(-)(1). The vibrational frequencies were compared with gas-phase frequencies and with density functional theory (DFT) calculations. Furthermore, the lowest vibrational levels of the (1)Pi(u) state of Cs(2) isolated in solid argon were observed by Raman matrix spectroscopy.