On the submillimetre wave refraction of liquids

It is shown that the refractive index associated with a heavily damped Lorentzian oscillator of low resonant frequency is radically different in spectral form from that found for the more familiar lightly damped oscillator. The complex refraction spectrum of a crude model consisting of three such overlapping oscillators of equal strengths and linearly spaced resonant frequencies shows a striking qualitative resemblance to the observed submillimetre spectra of liquids. The consistency of the agreement for both refraction and absorption supports the suggestion of Hill that a more sophisticated model involving the superposition of a range of heavily damped resonances is applicable to these liquid spectra.