title: Excitation levels and magic numbers of small parahydrogen clusters (N<or=40).
abstract: The excitation energies of parahydrogen clusters have been systematically calculated by the diffusion Monte Carlo technique in steps of 1 molecule from 3 to 40 molecules. These clusters possess a very rich spectra, with angular momentum excitations arriving up to L=13 for the heavier ones. No regular pattern can be guessed in terms of the angular momenta and the size of the cluster. Clusters with N=13 and 36 are characterized by a peak in the chemical potential and a large energy gap of the first excited level, which indicate the magical character of these clusters. From the calculated excitation energies, the partition function has been obtained, thus allowing for an estimate of thermal effects. An enhanced production is predicted for cluster sizes of N=13, 31, and 36, which is in agreement with the experiment.
authors.affiliation: Departamento de Física Atómica y Nuclear, Facultad de Física, 46100 Burjassot, Spain.
authors.forename: Rafael
authors.initials: R
authors.lastname: Guardiola
authors.forename: Jesús
authors.initials: J
authors.lastname: Navarro