Ion-Phosphate Mode in the DNA Low-Frequency Spectra
  The vibrational dynamics of a DNA molecule with counterions neutralizing the charged phosphate groups have been studied. With the help of elaborated model the conformational vibrations of the DNA double helix with alkaline metal ions have been described both qualitatively and quantitatively. For the complexes of DNA with counterions Li+, Na+, K+, Rb+ and Cs+ the normal modes have been found, and a mode characterized by the most notable ion displacements with respect to the DNA backbone has been determined. The frequency of counterion vibrations has been established to decrease as the ion mass increases. The results of theoretical calculation have been showed to be in good agreement with the experimental data of Raman spectroscopy. 
S. M. Perepelytsya, S. N. Volkov