Measurements of the mass abundance spectra of sodium clusters containing up to 600 atoms are presented. The clusters are produced in a seeded supersonic expansion of Ar or Kr gas, and the spectra are obtained by a time-of-flight technique. The sawtooth features in the spectra are interpreted as evidence of a regular spherical shell structure with magic numbers, N O , scaling approximately with the cube root of the number of sodium atoms. Altogether twelve shell closings are observed, N o = 2, 8, 20, 40, 58, 92, 138, 196, 260, 344, 440 and 558. There is also a pronounced odd-even staggering all the way up to N = 70. The experimentally observed intensity changes for the clusters around the magic numbers are discussed in terms of the electronic free energy, F(N), calculated at finite temperature, and the second differences of the free energy A2F(N ) = F(N -1) -2F(N) + F(N + 1). The processes behind the non-uniform abundance distributions, and the thermodynamics of finite electron systems with non-uniform level spacings are discussed on this basis.

Weltraumchemie: Die Bindung zwischen C60+ und (H2O)4 in einem geladenen Komplex aus C60 und dem H2O‐Tetramer in Heliumnanotröpfchen (siehe Bild) ist überraschend schwach. Doppelt geladene C602+‐Intermediate könnten durch Ladungstransfer mit He+ entstehen; sie können Ion‐Molekül‐Reaktionen auslösen, die bei der Molekülsynthese in interstellaren Wolken und im Sonnennebel eine Rolle spielen könnten.

We investigate two reaction channels of C 60 , excited by a pulsed laser at 355 nm: i) The relative and absolute yields of even-sized fragment ions are measured over a wide range of laser fluences. At low fluence we find a dramatic dependence of the abundance ratio of C + n−2 versus C + n . This result argues against the notion that unimolecular emission of C 4 or larger fragments contributes significantly to the production of even-sized fragment ions. ii) We count the number of delayed electrons emitted from C 60 , or one of its products, after photo-excitation. For high laser fluences, this number reaches a value of (2.6 ± 1.1) % per photoexcited C 60 . This sets a lower bound to the ratio of effective rate constants, k e (E * )/ k j (E * ), where k e refers to electron emission, and the sum in the denominator extends over all reaction channels.

Complexes of atomic gold with a variety of ligands have been formed by passing helium nanodroplets (HNDs) through two pickup cells containing gold vapor and the vapor of another dopant, namely a rare gas, a diatomic molecule (H2, N2, O2, I2, P2), or various polyatomic molecules (H2O, CO2, SF6, C6H6, adamantane, imidazole, dicyclopentadiene, and fullerene). The doped HNDs were irradiated by electrons; ensuing cations were identified in a high-resolution mass spectrometer. Anions were detected for benzene, dicyclopentadiene, and fullerene. For most ligands L, the abundance distribution of AuLn+ versus size n displays a remarkable enhancement at n = 2. The propensity towards bis-ligand formation is attributed to the formation of covalent bonds in Au+L2 which adopt a dumbbell structure, L-Au+-L, as previously found for L = Xe and C60. Another interesting observation is the effect of gold on the degree of ionization-induced intramolecular fragmentation. For most systems gold enhances the fragmentation, i.e., intramolecular fragmentation in AuLn+ is larger than in pure Ln+. Hydrogen, on the other hand, behaves differently, as intramolecular fragmentation in Au(H2)n+ is weaker than in pure (H2)n+ by an order of magnitude.