Emission spectra resulting from clustering reactions of a rare gas ion Rg(+)(Rg=Ne,Ar,Kr) with a heavier rare gas Rg'(Rg'=Ar,Kr,Xe) have been studied in rare gas flowing afterglows at various stagnation pressures of Rg'. At low stagnation pressures of Rg', emission spectra of NeRg'(+) (Rg'=Ar,Kr,Xe), ArRg'(+)(Rg'=Kr,Xe), and KrXe+ heterodimer ions were found due to radiative association and three-body clustering reactions, At high stagnation pressures of Rg'. new continuous bands were found at the longer-wavelength region of the heterodimer bands in most cases. They were attributed to bound-free transitions of NeRg(2)'(+)(Rg'=Ar,Kr,Xe), ArRg(2)'(+)(Rg'=Kr,Xe), and KrXe2+ heterotrimer ions. In most cases, the RgRg(2)'(+) bands consisted of two components: the first continuum degraded to the red from near the B 1/2-X 1/2 and C-1 3/2-A(1) 3/2 transitions of the RgRg'(+) bands, and the second continuum, a roughly Gaussian feature at longer wavelengths. It was found that the lower Rg(+)(P-2(3/2)) components were responsible for the formation of RgRg(2)'(+*). The first and the second components were ascribed to the B1/2-X1/2 and/or C-1 3/2-A(1) 3/2 transitions and the B 1/2-A(2) 1/2 transition of RgRg(2)'(+), respectively. The emission intensity of the second continuum increased more rapidly than that of the first one with increasing the stagnation pressure of Rg' or a foreign gas. It was explained as due to the fact that the first continuum arises from highly vibrationally excited levels near the dissociation Limits, while the second one occurs dominantly from low vibrationally excited levels formed by collisional relaxation of the upper vibrationally excited levels. (C) 1997 American Institute of Physics.