Alkali-Metal Promotion of a Dissociation Precursor:N2on Fe(111)

Abstract

The vibrational and thermal-desorption spectra of the terminal and $\pi$-bonded adsorption states of ${\mathrm{N}}_2$ on clean and potassium-promoted Fe(111) at 74 K are reported. Submonolayer precoverages of potassium dramatically enhance the sticking coefficient of ${\alpha }_1-{\mathrm{N}}_2$, the $\pi$-bonded precursor to dissociation. As potassium promotion of surface reactions has been previously attributed to bond weakening in the dissociation precursor, an increase of the precursor population, with no evident bond weakening, is an important new result.