A vibrational spectroscopy study on the interaction of N2 with clean and K-promoted Fe(111) surfaces: π-bonded dinitrogen as precursor for dissociation

The interaction of N2 with an Fe(111) surface was investigated by high resolution electron energy loss spectroscopy. The molecular α1-N2 state on the clean surface is identified as the immediate precursor for dissociation, and is characterized by a much reduced N-N stretch frequency of 1490 cm− (15N2) which resembles those with an N-N bond order of ~ 2. The bonding geometry for this species is therefore proposed to be side-on with both N atoms coordinated to Fe atoms. In the vicinity of K atoms, the adsorbed N2 (α2-state) bears a higher adsorption energy and a further reduced N-N stretch frequency (down to 1370 cm−1 for 15N2). The effect of co-adsorbed K atoms could be rationalized in terms of an enhanced back-donation from metal d-orbitals to the N2 π∗-antibonding orbital.