COVERAGE-DEPENDENT BOND-LENGTH OF CHLORINE ADSORBED ON CU(111)

The adsorption of Cl-2 on Cu{lll} at 300 K has been studied using shad ow-cone-enhanced secondary ion mass spectrometry (SIMS). The system ha s been investigated for chlorine coverages ranging from 0.08 to 0.33 m onolayer (ML), including the Cu{lll}-(root 3 x root 3)R30 degrees-Cl s urface. The secondary Cu+ ion intensity has been measured as a functio n of the incidence angle of the primary ion beam. The enhanced intensi ty features in the spectra are compared with results from a two-body i nteraction calculation that uses the Moliere approximation to the Thom as-Fermi potential. A chlorine-copper interlayer spacing of 1.87 +/- 0 .04 Angstrom is measured between the coverages of 0.17 and 0.33 ML. Th is value corresponds to a chlorine-copper bond length of 2.38 +/- 0.04 A, At 0.08 ML, the chlorine-copper bond length is expanded to 2.48 +/ - 0.04 Angstrom. These results suggest that the chlorine-copper bond i s more ionic in the low coverage limit.