Interpretation of x-ray emission spectra: NO adsorbed on Ru(001)

A density functional investigation of the x-ray emission spectrum of NO ads orbed on Ru(001) has been carried out using model cluster calculations. The dipole matrix elements governing the emission probability were evaluated i n the frozen ground-state approximation. The resulting simulated spectra ex hibit all characteristic features of the experimental data. A detailed anal ysis of the electronic structure of the model clusters permits a complete r ationalization of all observed trends. Furthermore, a picture of the surfac e chemical bond results in which the classical Blyholder frontier orbital m odel is extended to a three-orbital description for both the pi and sigma i nteractions. Comparison of different adsorption sites reveals that threefol d coordinated NO features a stronger orbital interaction with the substrate than NO adsorbed in an on-top position. (C) 1999 American Institute of Phy sics. [S0021-9606(99)01434-8].