Femtosecond Interatomic Coulombic Decay in Free Neon Clusters: Large Lifetime Differences between Surface and Bulk

A quantitative determination of $2s$ vacancy lifetimes in surface and bulk atoms of free Ne clusters has been made. While for free atoms the $2s$ inner-valence hole has a ps lifetime, it reduces to $6\pm 1\mathrm{f}\mathrm{s}$ for cluster bulk atoms. For surface atoms, the lifetime is on average longer than 30 fs. The lifetime estimate was obtained from fits of high-resolution photoelectron spectra of Ne clusters. The shortening of the lifetime is attributed to the coordination dependent interatomic Coulombic decay, which is extremely sensitive to internuclear distances.

Figure 1

Photoelectron spectrum of the Ne $2s$ level of cluster with $⟨N⟩\approx 900$. The spectrum is presented on a logarithmic intensity scale to emphasize the tails of the features. In the main part, a fit using a Voigt line profile is presented, and in the inset a Gaussian line profile is used. The regions which are not well described by the Gaussian line profile are shaded in the inset. The full width at half maximum of the atomic line, at 0 eV relative binding energy, is 30 meV, which is determined by the instrumental broadening.

Figure 2

Photoelectron spectrum of the Ar $3s$ level for clusters of size $⟨N⟩\approx 2000$. The spectrum is presented on a logarithmic intensity scale. The sharp peak at 0 eV relative binding energy comes from uncondensed atoms. The line shape of the cluster features is almost perfectly Gaussian, in contrast to Ne $2s$.

Figure 3

Photoelectron spectra of the Ne $2s$ level for clusters of varying sizes, recorded with an experimental resolution of 50 meV. The spectra have been normalized to give the cluster feature at higher binding energy the same intensity. The lower binding energy peak increases with increasing size, indicating that it originates from interior atoms. The cluster features also shift to lower binding energy with increasing size.