Local vibrational modes of natural isotopes of substitutional oxygen in CdTe

We investigated the localized vibrational modes LVM of natural oxygen containing $^{16}$O, $^{17}$O, and $^{18}$O isotopes at a substitutional tellurium site in cadmium telluride using infrared absorption spectroscopy at cryogenic temperatures. The main absorption peak observed at 350 cm$^{-1\, }$was formerly attributed to a fundamental LVM mode $\nu _{0} $ of oxygen at a tellurium site. The relatively weak absorption peaks observed at 331 cm$^{-1\, }$and 340 cm$^{-1\, }$are assigned as the same $\nu_{0}$ mode of the $^{17}$O and $^{18}$O isotopes, respectively, based on their relative intensities and spectral positions. The spectral positions were confirmed with theoretical calculations using a linear chain model where the peak position at 350 cm$^{-1}$ was taken as the reference for the $^{16}$O isotope. From a least square analysis of the observed peak positions we were able to calculate the force constants from perturbation theory. A Lorentzian line shape analysis of each $\nu_{0}$ absorption peak, considering the effects of isotopic mass and natural abundance variations of the host Cd atoms, was also carried out to further confirm their assignments. Reasonably good line shape fittings were obtained for $\nu _{0}$ modes of all isotopes of oxygen.