Small oscillations of test particles with angular momentum in   Reissner-Nordstrom field
  The oscillations of the test particles on circular orbits in field of super-extremal charged central object are researched. The formulae for oscillation frequencies are obtained in cases of circular orbits perturbations caused by small change in energy of the particle or by the small change in mass of the central object. 
Valentin D. Gladush and Alexander I. Petrusenko
gr-qc