Atom-selective bond breaking in a chemisorbed homonuclear molecule inducedby core excitation: N-2/Ru(001)

We observe photochemical selectivity for N 1s to pi* excitations of chemiso rbed N-2. By narrow bandwidth synchrotron radiation we selectively excite o ne of the two atoms of the molecule. Photon stimulated desorption of neutra l N atoms predominates for excitations of the N atom close to the surface, whereas excitation of the outer atom ejects predominantly N-2(0) and small amounts of N+, demonstrating the predominant breaking of the inner or outer bond, respectively, of the N-2 adsorbate. Analysis on the basis of previou sly obtained decay electron spectra after atom-selective excitation can exp lain the mechanism of localized bond breaking.