Laser-vaporized platinum metal, trapped in solid Ne, Ar, Kr, Xe (and Ar, Kr mixture) produced a progression of absorption bands with a spacing of similar to 200 cm(-1) beginning at 1942 cm(-1) in Ne and shifting successively to 1579 cm(-1) in Xe. In contrast with the specimen in Ne, strong patterns of similar sidebands appeared in the spectra in the heavier matrices. This matrix effect is considered in some detail in attempting to assign the trapped molecule and to explain the source and structure of the sidebands. The conclusion is that the absorption spectrum is the previously unobserved (3) Pi(u)(1(u))<--X (3) Sigma(g)(-)(0(g)(+)) transition of Pt-2 (inferred from Balasubramanian’s calculation) but with unique phonon interactions in the heavier matrices. When hydrogen was present in the matrix gases, Pt hydride bands were observed but not prominently, in contrast to Ni+H-2 matrices.