  A closed expression is derived for the pair vibrational correlation energy
generated in the random phase approximation by the isovector pairing force in
the case when Kramers and charge degenerate single-nucleon levels are uniformly
distributed in an interval. The expression is used to analyze the spectral
density of pair vibrational frequencies relative to that of two-quasinucleon
energies. Applications to the analysis of the symmetry energy of the isovector
pairing model and to a Strutinskij renormalization of this model are discussed.
