Photoionization Yields, Appearance Energies, and Densities of States of Copper Clusters

• Published in: Journal of physical chemistry. C Vol. 119; no. 20; pp. 11178 - 11183
• Main Authors: Halder, Avik, Huang, Chuanfu, Kresin, Vitaly V
• Format: Journal Article
• Language: English
• Published: American Chemical Society 21.05.2015
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/jp511940z

We present the results and analysis of photoionization measurements of neutral Cu n=24–98 clusters, thermalized to T = 60 and 215 K. The photoion yield curves were used (1) to determine the cluster ionization appearance energies via a fit to the Fowler law of surface photoemission and (2) to explore the suitability of these curves for accessing information about electron states lying below the ionization threshold. The appearance energies follow a standard shell pattern up to n ≈ 40, but a subsequent structure suggests that the electronic shells become perturbed and split by crystal field effects. Nevertheless, it is apparent that the spectra are determined essentially by the number of delocalized electrons, i.e., by the sequential filling of electronic shell sublevels. The average shift of the appearance energies with cluster temperature was found to be in good agreement with a theoretical prediction for bulk copper. An important finding is that the derivatives of the ion yield curves overlap well with the photoelectron spectra of isoelectronic cluster anions. This means that accurate photoionization yield curves of cold clusters can be used to trace their subthreshold electronic densities of states.