Fine structure of the asymmetric stretching vibration of dispersed oxygen in monoisotopic germanium

Dispersed oxygen in Ge leads to the formation of Ge₂O ``quasimolecules'' whose asymmetric stretching mode (ν₃), exhibits a remarkable, temperature-dependent fine structure when examined under the ultrahigh resolution of a Fourier-transform spectrometer. The large number of sharp lines observed arises from the coupling of ν₃ with the low-energy symmetric bending ν₂ mode; the thermal population of the ν₂ levels, together with the shifts associated with the isotopes of Ge in their natural abundances, underlie its fine structure and temperature dependence. By incorporating oxygen in monoisotopic ⁷⁰Ge, ⁷³Ge, ⁷⁴Ge, or ⁷⁶Ge, the excitation spectrum of the ν₂+ν₃ coupling is selectively simplified. From the temperature dependence of the intensities of the lines in the fine structure, the energies of the ν₂ levels are deduced. The ¹⁸O counterpart of the ν₂+ν₃ coupling excitation has been observed and a consistent interpretation of the ν₂ levels as well as the shifts of the ν₂+ν₃ coupling excitations associated with any isotopic combination of oxygen and Ge is obtained by using an interaction mass m'=23.1 amu and a Ge-O-Ge bond angle 2{α}=111^∘{}.