DIRECT EVIDENCE FOR CHARGE-TRANSFER PHOTODISSOCIATION AT A METAL-SURFACE - CCL4/AG(111)

Observation of negative ions desorbing from an adsorbate-covered metal surface following UV laser irradiation gives direct evidence that the mechanism responsible is charge-transfer photodissociation (CT-PDIS). We have studied photoemission of ions for CCl4/Ag(111) + hv --> Cl-(g) + CCl3/Ag(111). The CT-PDIS mechanism is supported by comparison of the yield of desorbing Cl- and photoemitted electrons with the variation in UV photon energy and surface coverage. Charge transfer leading to negative-ion emission is also shown to occur in the absence of photoelectron emission (i.e., hv < phi) for CCl4/Ag(111).