Size- and temperature-dependent structural transitions in gold nanoparticles were revealed with morphology statistics obtained by high-resolution electron microscopic observations for thousands of particles annealed in a helium heat bath. We found that gold nanoparticles over a wide size range, 3-14 nm, undergo a structural transformation from icosahedral to decahedral morphology just below the melting points. It was also clarified that the formation of bulk crystalline structures from the decahedral morphology requires the melt-freeze process due to an insurmountable high free-energy barrier.

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The energy profile of the interconversion path between the T-shape and slipped-parallel dimers has been studied by high level ab initio calculations. The CCSD(T) (coupled cluster calculation with single and double substitutions with noniterative triple excitations) interaction energy at the basis set limit has been estimated from the MP2 (the second-order Møller–Plesset calculation) interaction energy near the basis set limit and the CCSD(T) correction term using the 6-311G* basis set. The calculated CCSD(T) level energy profile has shown that the potential is very flat and the interconversion barrier height is very small (around 0.2 kcal/mol). The MP2 calculations using large basis sets near the basis set limit considerably overestimate the attraction of the slipped-parallel dimer, which indicates the importance of higher level electron correlation correction for studying the potential energy surface of the benzene dimer.

The infrared depletion spectrum of the aniline dimer, formed in a supersonic jet, has been recorded in the N−H stretch region by combining infrared laser excitation and resonant two-photon ionization/time-of-flight mass spectrometry. Only two bands have been found at 3394.0 and 3465.9 cm-1 (±0.5 cm-1) in the region 3130−3530 cm-1. These are red-shifted by 27.8 and 42.3 cm-1 from the symmetric and asymmetric NH stretching vibrations of the aniline monomer, respectively. A configuration with mutual NH2···π bonds and phenyl groups stacked in parallel is suggested for the ground-state aniline dimer.

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Collision induced dissociation of Cun+ clusters (n=2–9) in collision with Xe is presented in the center-of-mass energy range from about 100 meV to above 15 eV. The collision energy dependence is measured for the total and the partial dissociation cross sections, and the dissociation thresholds for the dominating processes are derived. The threshold energies show pronounced odd–even alternations, reflecting a higher stability of the odd-numbered, Cu2n+1+, clusters. Further, the evaporation of a single neutral atom is found to be the energetically favorable process for the even-numbered clusters, while the loss of the neutral dimer is favorable in the case of the odd-numbered clusters. An exception is Cu9+, where the formation of Cun−1+ is energetically favorable, and the energetics of the Cun−2+ formation are in good agreement with sequential evaporation of two neutral monomers. Here we discuss the energy dependency of the total and partial dissociation cross sections, and try to give a consistent picture of the dissociation dynamics. We present binding energies for the cationic clusters from their dissociation thresholds, and use those, in combination with the literature values for the ionization potentials of Cun, to estimate the binding energies for neutral copper clusters. Finally, we compare this work to earlier theoretical calculations, as well as experimental estimations of the binding energies.

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The reactions of gold cluster cations Aun+ (n=1–12) with H2S and H2 have been studied using Fourier-transform ion-cyclotron resonance (FT–ICR) mass spectrometry. The cluster cations were produced by laser ablation of a gold rod in He atmosphere, and their reactions were observed at room temperature and low total pressures of 10−7–10−5 Torr. Initial products of the reactions with H2S were mainly AuSH+ for n=2, AunS+ for n=4–8 and 10, and AunSH2+ for n=9, 11, and 12. No reactions of Au+ and Au3+ with H2S were observed. Even n cluster cations were more reactive than adjacent odd n clusters. The particularly low reactivity at n=1, 3, 9, and 11 is consistent with the low ionization potential of Aun and the weak binding energy of Aun+–Au. Further sulfuration reactions of AunS+ proceeded to give AunSm+ and finally stopped at AunSm+xH2+ when H2 release did not occur. The maximum number of sulfur atoms m+x increased with the cluster size up to n=8, while the sulfuration reaction stopped at early stages for n⩾9. In another series of experiments, no reaction of Aun+ (n=1–12) with H2 gas pulses introduced into the FT–ICR cell was observed. To investigate the stability of gold hydride clusters, laser ablation of gold in a H2/He mixture was performed. The hydride cluster cations AunHm+ were produced for n=1–7, while bare Aun+ clusters were the main products for n⩾8. There is a distinct border between n=7 and 8, as the structure of Aun+ changes from planar for n⩽7 to three-dimensional for n⩾8, suggesting the stability of hydride cluster cations with planar gold frameworks.