Surface x-ray-diffraction study of the Rh(111)+(2x2)-3CO structure

We have studied the geometry of the high-coverage Rh(111) + (2 x 2)-3CO str ucture by surface x-ray diffraction. Analysis of the in-plane data set reve als three evenly separated CO molecules per (2 x 2) unit cell. The evaluati on of the crystal truncation rods shows that one CO molecule resides in an- on-top site while the other two CO molecules occupy hollow sites. The inten sity modulations of the out-of-plane fractional order rods provide geometri cal information about distances between the C and O atoms and on the buckli ng of the CO overlayer. [S0163-1829(99)10107-3].