Niveaux collectifs de noyaux pairs-pairs excités par diffusion de particules α

We have studied 44 MeVα-particle inelastic scattering by 48Ti, 58Fe, 62Ni, 64Ni. Angular distributions are able to determine parity, sometimes spin and the deformation parameter of onephonon levels. We obtain also information on double nuclear excitation. With these results and those previously obtained we can draw a general picture of the collective excitation in the 22 ≤ Z ≤ 30 region.La diffusion inélastique de particules α de 44,0 ± 0,2 MeV par 48Ti, 58Fe, 62Ni, 64Ni a été étudiée. L'analyse des distributions angulaires permet de déterminer la parité, et quelquefois le spin et le paramètre de déformation pour les niveaux à un phonon, et d'obtenir des renseignements sur le comportement des niveaux relevant de la double excitation nucléaire. Ces résultats, joints à ceux obtenus antérieurement, permettent de dresser un tableau général de l'évolution des excitations collectives dans la région 22 ≤ Z ≤ 30

Mechanical Vibrations of Atomically Defined Metal Clusters: From Nano- to Molecular-Size Oscillators

Acoustic vibrations of small nanoparticles are still ruled by continuum mechanics laws down to diameters of a few nanometers. The elastic behavior at lower sizes (n(SR)m with a number n of atoms ranging from 10 to 102 (0.5–1.5 nm diameter range). Two periods, corresponding to fundamental breathing- and quadrupolar-like acoustic modes, are detected, with the latter scaling linearly with cluster diameters and the former taking a constant value. Theoretical calculations based on density functional theory (DFT) predict in the case of bare clusters vibrational periods scaling with size down to diatomic molecules. For ligand-protected clusters, they show a pronounced effect of the ligand molecules on the breathing-like mode vibrational period at the origin of its constant value. This deviation from classical elasticity predictions results from mechanical mass-loading effects due to the protecting layer. This study shows that clusters characteristic vibrational frequencies are compatible with extrapolation of continuum mechanics model down to few atoms, which is in agreement with DFT computations