Core-level electron spectroscopy on the sodium dimer Na $2p$ level

The lifetime broadening and molecular field splitting of the sodium dimer $2p$ core level is studied by x-ray photoelectron spectroscopy and by Auger electron spectroscopy. The lifetime of the Na $2p$ core hole has been determined to be $15\pm 8\mathrm{fs}$, much shorter than what has previously been reported for solid sodium. The molecular field splitting of this core level has been determined to be $42\pm 10\mathrm{meV}$. The Auger measurements have experimentally confirmed that the sodium dimer is a good example of when the Coulomb explosion mechanism determines the spectral shape.

Figure 1

Time-of-flight spectrum of the metal-vapor beam. The main contribution is atomic, but there is also a substantial amount of dimers. No large contribution from trimers is seen.

Figure 2

Photoelectron spectrum of the Na $2p$ region. The features between 37.8 and $38.7\mathrm{eV}$ are atomic lines, the features between 36 and $36.3\mathrm{eV}$ are the dimer lines.

Figure 3

The spin-orbit split sodium dimer photoelectron lines. The dots represent the experimental data, the dashed lines are the fit components, the whole line is the sum of the fit components and the vertical bars are the calculated vibrational progressions. The molecular field splitting is marked $E_m$.

Figure 4

Auger spectrum showing the dissociative dimer contribution. The features to the left and right of the dimer feature stem from atomic Auger decay.

Figure 5

Schematic picture of the Auger linewidth estimation. The effective Franck-Condon region is projected onto the Coulomb potential, which allows for a direct read-out to the Auger width.