  The ICARUS and future liquid argon neutrino experiments generate demand for
evaluating the spectral function of argon. In this paper we use oxygen nucleus
as a testing ground for our phenomenological approach to the spectral function
and probe the influence of momentum distribution and treatment of the mean
field spectral function on the differential cross sections. The obtained model
reproduces very well results of the exact spectral function of oxygen and can
be applied to heavier nuclei, such as calcium or argon.
