Abstract
When electronically excited CO(a(3)Π) collides with a Au(111) surface, electron emission can be observed with a quantum efficiency of 0.13. We have studied the influence of Ar, Kr and Xe adsorption on the electron emission efficiency resulting from CO(a(3)Π) quenching. Surprisingly, a single monolayer (ML) of rare gas dramatically enhances electron emission. For Ar and Kr bilayers, emission efficiency is further enhanced and approaches unity. The quenching mechanism involves electron transfer from the metal to the CO(a(3)Π) molecule followed by electron emission from the molecule. The enhanced emission efficiency is due to the long range nature of the initial electron transfer process and the rare gas adlayer's ability to reflect the electron emitted by the transient CO anion. This work shows that CO(a(3)Π) quenching is a useful model system for investigating the fate of electronically excited molecules at surfaces.
Highlights
When electronically excited molecules collide with metal surfaces, electron transfer (ET) between surface and molecule often occurs, which can be accompanied by electron emission into vacuum.[1,2,3,4,5]
We studied the interaction of electronically excited CO molecules in the a3P state – hereafter referred to as CO* – with a Au(111) surface using molecular beam surface scattering experiments.[3,4]
We investigated interfacial electron transfer and charge separation by scattering CO molecules in their a3P state from rare gas covered Au(111)
Summary
When electronically excited molecules collide with metal surfaces, electron transfer (ET) between surface and molecule often occurs, which can be accompanied by electron emission into vacuum.[1,2,3,4,5] We studied the interaction of electronically excited CO molecules in the a3P state – hereafter referred to as CO* – with a Au(111) surface using molecular beam surface scattering experiments.[3,4] CO* molecules exhibit an internal electronic excitation energy of 6.0 eV, and electron emission is observed when CO* collides with a Au(111) surface with a work function FAu = 5.3 eV.[3]. The electron transfer efficiency from the metal to the molecule and the lifetime of the resulting anion depend strongly on the distance between surface and molecule. There has been little work describing the influence of the spacer layer on electron emission efficiency
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