Electron Attachment TOF Oddný Þorbergsdóttir, Oddný Ragnarsdóttir, and Linda Hancock

Introduction Theory & Background What is electron attachment? Electron Affinity & Bond Order Bound-to-Bound Transitions Bound-to-Repulsive Transitions Application Instrumentation Results

Dissociative electron attachment (DEA) Interactions between low-energy electrons with gas phase molecules below the first Ionization energy threshold of the molecule Categorized as: i) Non-resonant scattering e- + M  M* + e- ii) Resonant electron capture; the formation of a transient negative ion (TNI) e- + M  M-(*)

Electron affinity The energy difference between M and M- in their ground states. By convention: EA > 0 ; then E(M-) < E(M) EA <0 ; then E(M-) > E(M) E(M) / E(M-) : the molecules are in their ground state.

For O2: fewer unpaired e, more stable molecule even though we increase the distance between the orbitals sigma and simga* (s) orbitals repell each other and O2 has extra protons which push the sigma (2s) down.

Bound-to-Repulsive State Transition Diagram represents dissociative electron attachment (DEA): M-(*)  A + B- or A- + B When the electron is attached to the molecule (excited state OR not excited) it enters a repulsive state because the electron is in an antibonding orbital which lowers the bond order (in most cases) The ion yield from this reaction represents the probability of this transition

Instrumentation Ionization Source: Electron beam is controlled by the electron monochromator Adjustable voltages Sample Intro: Molecular beam (gas phase) Ion Separation: TOF tube Transducer: Ion counter Ions create current~counts

Instrumentation Electron monochromator TOF Tube (Field-Free Region) Ion Counter Instrumentation

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