EELS of negative-ion resonances: N-2 films on Ag(110) at 15 K

The growth and structure of solid nitrogen films on Ag(110) at 15 K was investigated by means of high-resolution electron energy loss spectroscopy (EELS), thermal desorption spectroscopy (TDS) and low-energy diffraction (LEED). The N-2 film exhibits a parallelogram structure with the lattice constants b(1) = 3.85 Angstrom, b(2) = 4.34 Angstrom and gamma = 70.5 degrees in the monolayer. For multilayers, an incoherent hexagonal structure with a lattice constant b = 4.02 Angstrom has been found. For a coverage of 5.3 ML, the negative ion resonances (NIR) have been investigated by EELS. For the (2) Pi(g) resonance, the excitation function shows a maximum at similar to 2.7 eV, and the angular emission profile exhibits a maximum at similar to 42 degrees. The overtone excitation of the N-N stretching vibration is strongly enhanced, and the high-energy tail originates from combined and multiple losses. The sigma(u) resonance at 19.0 eV leads to a strong excitation of both the N-N stretching vibration and the associated overtones. In addition, strong excitations of electronic states have been observed.