Charge-transfer photodissociation of adsorbed molecules via electron image states

TL;DR

This study demonstrates that charge-transfer photodissociation of adsorbed halomethanes occurs via electron image states, where photoelectrons are temporarily trapped and transfer charge to induce dissociation.

Contribution

It reveals a new mechanism involving electron image states mediating photodissociation of adsorbed molecules on a substrate.

Findings

Dissociation is caused by dissociative electron attachment from sub-vacuum level photoelectrons.

Photodissociation characteristics depend on coverage and energy distributions.

Charge transfer occurs through an image potential state near the interface.

Abstract

The 248nm and 193nm photodissociation of submonolayer quantities of CH$_3$Br and CH$_3$I adsorbed on thin layers of n-hexane indicate that the dissociation is caused by dissociative electron attachment from sub-vacuum level photoelectrons created in the copper substrate. The characteristics of this photodissociation-- translation energy distributions and coverage dependences show that the dissociation is mediated by an image potential state which temporarily traps the photoelectrons near the n-hexane--vacuum interface, and then the charge transfers from this image state to the affinity level of a co-adsorbed halomethane which then dissociates.