Near-threshold photoionization of germanium clusters in the 248–144nm region: ionization potentials for Ge_n

Abstract

We examine the photoionization thresholds of Ge _n (n = 2–34) with a wide photon energy (5.0–8,6 eV) using a laser photoionization time-of-flight mass spectrometry. A high-output vacuum ultraviolet light generated with stimulated Raman scattering is used as the ionization light source in the energy above 6.0 eV. A characteristic size dependence of ionization potential (IP) with a maximum at n = 10 is found for clusters smaller than 22 atoms. The rather high IP of Geio in comparison with its neighbors is consistent with the results on the photodissociation study of Get. We also find that IPs decrease rapidly from n = 16 to 22, and then decrease at a much slower rate for larger clusters. These features in IPs are similar to those of S1 _n reported in our previous paper, except for the smaller IP gap of Ge⁺ _n at n ≈ 20. We discuss these results on IPs in relation to their electronic structure and stability.