Absence of an Isotope Effect in the Two Level Spectrum of Amorphous Ice

We have measured the low temperature far infrared absorption in the high and low density amorphous phases of ${\mathrm{H}}_2\mathrm{O}$ and ${\mathrm{D}}_2\mathrm{O}$ in the region $2–30{\mathrm{cm}}^{-1\mathrm{}}$. For each isotope, resonant absorption by two level systems is observed for the high density amorphous phase but not for the low density amorphous one. In addition, within our experimental uncertainties no isotope effect is detected in the strength or extent of the two level spectrum in the high density phase.