Spectroscopy of tungsten oxide molecules in neon and argon matrices at 4° and 20°K

Abstract

WO, WO 2, and also WO 3, W 2O 6, W 3O 8, W 3O 9, W 4O 12 have been trapped in neon and argon matrices at 4° and 20°K and studied spectroscopically in the infrared, visible, and near-ultraviolet regions. The molecules were prepared by vaporization from the solid oxides at 1600°K or by passing 16O 2 or 18O 2 over tungsten at 1900 to 2950°K. Seven electronic transitions, lying between 3500 and 6000 Å, are observed in the absorption spectrum of WO. These progressions are generally found to be strongly perturbed in the W 16O spectra, but regular in W 18O. The strong system of bands with (0, 0) at 4807 Å in neon, observed in gas emission at 4806.4 Å, is essentially unperturbed in both molecules. The vibrational frequencies in the excited electronic states are determined and the various perturbations of the levels in W 16O discussed. The spectrum of WO 2 is similar to that of bent TaO 2 and exhibits two electronic transitions in a neon matrix at 7890 Å (strong) and 7806 Å (weak). A long progression of the bending frequency in the upper state appears in both systems indicating that the OWO angle undergoes a large change in the transitions. From the 7890-Å system, it is found that ν 1′ = 972, ν 2′ = 300 cm −1, ν 3′ = ?; the infrared spectrum yields ν 1″ = 992, ν 2″ = ?, ν 3″ = 928 cm −1. The MO schemes of TaO and TaO 2 are used to predict 3Σ − and 3A 1 ground states for WO and WO 2, and on this basis the excited states and assignment of electronic transitions are considered. A system of absorption bands beginning at 3452 Å in neon is tentatively assigned to WO 3. The larger molecules, WO 3, W 2O 6, etc., produce many bands in the infrared some of which can be assigned to particular oxide molecules by varying the conditions of vaporization.