The gas phase absorption spectra of the compounds OsO4and RuO4were measured between 2500 and 1050 Aring; with a Baird 1minus;m vacuum monochrometer of 1.0 Aring; bandwidth. Both tetroxides show many electronic absorption bands in this region with diffuse vibrational structure. No spectra of OsO4or RuO4have been previously reported below 2200 Aring;. Absorption maxima for OsO4, which were not previously reported, occur at 48 140, 63 620, 73 960, 85 620, 86 920, 89 160, 90 800, and 91 940 cmminus;1. The spectrum of RuO4showed band maxima at 50 660, 64 620, 72 700, 76 420, 79 040, 83 100, 88 860, and 92 080 cmminus;1. The general appearance and relative strengths of various absorption bands in the spectra of these molecules were similar, with the energy of apparently corresponding transitions shifted to the red in RuO4by approximately 10 000 cmminus;1. Most of the strong electronic transitions have been tentatively assigned on the basis of extended Huuml;ckel type calculations. The results of these calculations correlated reasonably well with the spectral data obtained. Bands are present in the spectra of both molecules which may be the first members of Rydberg series.
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