The optical transitions of adsorbates on metal surfaces, such as absorption (ABS), photoemission (PES) and inverse photoemission (IPS), are studied on the basis of the Newns-Anderson model supplemented with the screening due to the surface plasmons and charge transfer to/from the substrate. A brief description of the characteristic line shapes, including the absorption threshold in the ABS spectra and the final state charge transfer screening in the PES ones, is presented to demonstrate how an initially unoccupied state above the Fermi level plays a crucial role in the excited states of these optical transitions. In the IPS process, on the other hand, we find that an occupied level below the Fermi level in the neutral ground state screens the electron in the negative ion final states via the charge transfer to the metal, or remains occupied with a finite lifetime due to electron-hole pair excitations in the metal. These features manifest themselves in the double peak structure corresponding with the screened and unscreened IPS processes, or in the asymmetric line shape, depending on the position of the initially occupied level in the final state. The interference effect with the radiative transition into the metal unoccupied states is also investigated in conjunction with an another possible origin of the asymmetric IPS spectrum. The complementary aspects and certain common characteristics such as threshold, level shift and broadening of the ABS, PES and IPS spectra are investigated in detail. The energy diagrams of Xe atoms, and CO molecules on metal surfaces are presented by analysing those spectroscopic results, with which the theory is applied to calculate their ABS, PES and IPS spectra.