Oxygen-induced CO reorientation on Cr(110)

Abstract

Studies of CO and CO/O chemisorption on Cr(110) at 120 K using high resolution electron energy loss spectroscopy (EELS), electron stimulated desorption ion angular distributions (ESDIAD), low energy electron diffraction (LEED), and Auger electron spectroscopy (AES) are reported. On the clean surface, two molecular binding modes are sequentially populated. The first mode (α1CO) consists of molecules bound with the CO axis nearly parallel to the surface and saturates with the formation of a c(4×2) overlayer, whereas the second mode (α2CO) is comprised of CO oriented perpendicular to Cr(110). Predosing Cr(110) with atomic oxygen inhibits the α1CO mode such that for θ0 above ∼1/2 monolayer, only the α2CO mode is populated. More surprisingly, the c(4×2)α1CO overlayer is converted to disordered α2CO by subsequent addition of oxygen, implying a significant reorientation of the adsorbed molecules at 120 K.