Configuration change of NO on Cu(110) as a function of temperature

The bonding structure of nitric oxide (NO) on Cu(110) is studied by means of scanning tunneling microscopy, reflection absorption infrared spectroscopy, and electron energy loss spectroscopy at 6-160 K. At low temperatures, the NO molecule adsorbs at the short bridge site via the N end in an upright configuration. At around 50 K, this turns into a flat configuration, in which both the N and O atoms interact with the surface. The flat configuration is characterized by the low-frequency N-O stretching mode at 855 cm(-1). The flat-lying NO flips back and forth when the temperature increases to ~80 K, and eventually dissociates at ~160 K. We propose a potential energy diagram for the conversion of NO on the surface.