Vibrationally promoted electron emission from low work-function metal surfaces.

Area of Science:

• Surface Science
• Chemical Physics
• Materials Science

Background:

• Electron emission from molecule-surface interactions is crucial for understanding surface chemistry and catalysis.
• Previous studies typically show low electron yields for molecules in the ground vibrational state.

Purpose of the Study:

• To investigate electron emission from vibrationally excited nitric oxide (NO) molecules scattered from a cesium-dosed gold (Au) surface.
• To explore the relationship between vibrational excitation and electron emission efficiency.

Main Methods:

• Scattering vibrationally excited NO molecules (vibrational states 9 ≤ v ≤ 18) from a Cs-dosed Au surface.
• Measuring the quantum efficiency of electron emission as a function of the NO vibrational state (v).
• Analyzing the energy threshold for electron emission relative to the surface work function.

Main Results:

• Observed significant electron emission from vibrationally excited NO molecules, with quantum efficiency reaching 10⁻² electrons per NO(v) collision.
• Quantum efficiency increased strongly with increasing vibrational state (v), orders of magnitude higher than ground state values.
• Identified a threshold for electron emission where vibrational energy exceeded the surface work function, suggesting direct energy conversion.

Conclusions:

• Direct conversion of NO vibrational energy into electron kinetic energy is demonstrated.
• Provides evidence for non-adiabatic energy transfer events at metal surfaces involving large amplitude vibrational motion.
• Mechanisms such as vibrational autodetachment, Auger-type processes, and vibrationally promoted dissociation are considered.