Direct evidence for charge-transfer photodissociation at a metal surface: CCl_{4}/Ag(111)

Abstract

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 ${\mathrm{CCl}}_{4}$/Ag(111)+h\ensuremath{\nu}\ensuremath{\rightarrow}Cl-(g)+${\mathrm{CCl}}_{3}$/Ag(111). The CT-PDIS mechanism is supported by comparison of the yield of desorbing ${\mathrm{Cl}}^{\mathrm{\ensuremath{-}}}$ 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., h\ensuremath{\nu}) for ${\mathrm{CCl}}_{4}$/Ag(111).