Vibrational dynamics of polyurydilic acid

A study of the normal modes of vibration and their dispersion in polyurydilic acid (polyU) is reported using Wilsonʹs GF Matrix method as modified by Higgs. This is done for the `bareʹ as well as for the helix `loadedʹ with uracil. Confusion that has prevailed regarding the assignments of the observed modes at 810 and 572 cm−1 is cleared and it is shown that the so called bare helix (polyU-U) has a different minimum energy state and hence spectrally different. Dispersion of the normal modes in the two helices shows marked differences which are characteristic of the extent of electrical/mechanical coupling along the chain and between the chain and the base. Values predicted for the heat capacity as a function of temperature for polyU is also reported.