High-resolution electron energy loss spectroscopy and angle-resolved ultra-violet photoemission spectroscopy studies of carbon monoxide on a Cs-precovered Ru(101-bar0) surface

There are two molecular adsorption states of CO in the CO+Cs/Ru(101-bar0) system. One is α1-CO, with lower C-O frequency, and the other is α2-CO, with higher C-O frequency. The latter is similar to that on a clean Ru(101-bar0) surface. The two states of CO are occupied sequentially during the exposure to CO. The C - O stretch frequency of both states shifts to a higher value with the exposure to CO and to a lower value with higher Cs precoverage. The electronic structure of the α1-CO molecule is different from that of the α2-CO molecule and is of the same character as CO in a tilted mode. (author)