FAR-INFRARED SPECTRA OF MATRIX-ISOLATED URANIUM $OXIDES^{*}$

$^{*}$Work performed under the auspices of the U.S. Department of Energy.Author Institution:Infrared absorption spectra between 50 and $350 cm^{-1}$ have been obtained of $UO_{3}$ And $UO_{2}$ in argon matrices at 14 K. All three expected low-frequency vibrational modes of $U^{16}O_{3}$ have been identified and the frequencies measured for $\nu_{3}(A_{1})$, the in-plane bend; $\nu_{5}(B_{1})$, the in-plane wagging; and $\nu_{6}(B_{2})$, the out-of plane bend. The effects of $^{18}O$ substitution have been measured and interpreted to confirm these assignments. All results are consistent with a $C_{2v}$, T-shaped structure for the $UO_{3}$ molecule. The doubly degenerate bending modes of $U^{16}O_{2}$, $U^{16}{^{18}O}$, and $U^{18}O_{2}$ have been identified and their frequencies measured. The measured frequency and absorbance rations confirm these assignments