  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.
