CHEMISORPTION OF NO ON PT(111) STUDIED BY ARPES

The chemisorption of NO on a Pt(111) surface has been studied by angle -resolved photoelectron spectroscopy (ARPES). The NO molecular orbital s appear at 2.0 and 9.5 eV below the Fermi level after full coverage o f NO at 150 K. These molecular orbitals originate from 2 pi and 1 pi 5 sigma orbitals, respectively. The order of the 1 pi and 5 sigma orb itals of NO adsorbed on the Pt(111) surface is the reverse of that of gaseous NO. The 1 pi + 5 sigma orbital has a dispersion along the <(Ga mma)over bar>(K) over bar direction, with a width of about 0.4 eV and a maximum at 2/3 of the <(Gamma)over bar>(K) over bar period for the c lean Pt(111) surface. It suggests that the structure of the NO-adsorbe d Pt(111) surface has the 3/2 periodicity to the <(Gamma)over bar>(K) over bar direction, although the diffuse (2 x 2) structure is observed for the NO-adsorbed Pt(111) surface by law-energy electron diffractio n (LEED) at 150 K.