THE ADSORPTION OF N-2 ON NB(110) AT 80-K AND 20-K

The adsorption of N-2 on Nb(110) at 80 and 20 K has been studied by hi gh-resolution electron energy loss spectroscopy (EELS). At 80 K and lo w exposure N-2 is chemisorbed dissociatively. At higher exposure (abov e 2 L) molecular adsorption of N-2 is found. At 20 K and low exposure (<4 L) N-2 is chemisorbed in terminal position. The frequency of the N -N stretching vibration of chemisorbed N-2 has a value of 268 meV. At higher exposure (above 4 L) N-2 is physisorbed. The frequency of the N -N stretching vibration for physisorbed N-2 is 290 meV, which correspo nds to the Raman frequency of N-2 molecules in the gas phase. The line shape of the N-N stretching mode of the physisorbed N-2 molecules is asymmetric with a pronounced tail on the high-energy side.