Plasmon spectroscopy is first used to analyse the nanoscale-films’ surface of the transition metals. A detailed analysis of the plasmon energy loss spectra of primary electrons in the 50–600 eV range is carried out for surface layers of the nanoscale multilayer thin-film Ni(25 nm)/Cu(25 nm)/Cr(25 nm)/Si(001), Ni(25 nm)/Cu(25 nm)/V(25 nm)/Si(001) and V(25 nm)/Si(001) systems bombarded with low-energy Ar$^{+}$ ions and then held in a pure oxygen atmosphere. The mono- and multilayer systems obtained by the electron-beam deposition method in an ultrahigh vacuum of 10$^{-7}$ Pa are investigated. The samples are irradiated with Ar$^{+}$ ions with a current density of 5 $\mu$A/cm$^2$ and energy of 600 eV at doses of 2$\cdot10^{17}$ and 12$\cdot10^{17}$ ion/cm$^2$ and are kept in an atmosphere of atomically pure oxygen for 24 hours. The averaged values of energies of the surface ($E_{\textrm{s}}$) and bulk ($E_{\textrm{b}}$) plasmons, and their ratio $E_{\textrm{b}}/E_{\textrm{s}}$, the concentration of the conduction electrons participating in plasma oscillations, and the relative change in interplanar distances are calculated. The peaks of the surface and bulk plasmons observed in the nickel spectrum are localized at lower loss energies than they follow from the model of a homogeneous isotropic plasma of the set of the $s$ and $d$ electrons in accordance with the classical theory of collective excitations in a solid. The concentration of the conduction electrons is substantially reduced. In the case of vanadium, the maximum number of valence electrons participates in collective excitations. The concentration of such electrons is most strongly reduced for the surface that may be due to the structural features of the surface layers. After ion bombardment, the electron concentration decreases noticeably, probably because of formation of the radiation defects and due to the ‘expansion’-type relaxation of the crystal lattice for nickel or the ‘compression’-type relaxation for vanadium.