Samples of the solids MIO,(M= Li, Na, K, Rb, Cs) have been vaporized in vacuo and the ternary products characterized by mass spectrometry, and by infrared spectroscopy in low- temperature nitrogen, oxygen, and argon matrices. The molecular species KIO,, RbIO,, and CsI03 have been identified for the first time and their IR spectra shown to be consistent with overall C,, symmetry involving tridentate coordination. This conclusion is further confirmed, ...