Photodetachment studies of metal clusters: Electron affinity measurements for Cux

Abstract

Laser photodetachment studies have been performed on silver and copper cluster negative ion beams extracted from a supersonic metal cluster source. This source involves the use of laser vaporization within a pulsed nozzle to prepare the neutral cluster jet, followed by ArF excimer irradiation of the nozzle orifice as the copper clusters emerge into the expansion. Photoelectrons ejected from the aluminum nozzle by the excimer radiation are entrained in the supersonic flow and attach to the neutral copper clusters, producing negative ions which stabilize and extensively cool in the subsequent supersonic expansion. Laser photolysis of mass-selected negative copper cluster ions extracted from this source reveals efficient photodetachment to produce a free electron in the absence of measurable fragmentation. The laser fluence dependence of the photodetachment process at different photon energy permits a rough experimental determination of the electron affinities of copper metal clusters as a function of cluster size for the first time.

Laser photoionization and spectroscopy of gas phase silver clusters

“…An evenodd alternation in ionization potentials has been described for alkali metal clusters [8,9] and for copper [24,25]. Electron affinities for both copper and silver exhibit a similar even-odd alternation [10,24,26]. Ionization potentials, therefore, should exhibit a similar even-odd character for silver, but the exact details of these phenomena have not been reported previously.…”

“…In larger particulates of silver the unique optical properties are manifested in a low plasmon frequency, which is an essential feature in surface enhanced Raman spectroscopy at visible wavelengths. Previous studies on silver clusters include photofragmentation [13], reactivity [14], electron affinity measurements [15,26], and spectroscopy of small species [18,19]. Theoretical investigations are more tractable in the coinage metals than in open d-shell systems and therefore have been extensively pursued [20][21][22][23].…”

Gas-phase niobium cluster reactivity with isobutane

“…Ionization potential and electron affinity measurements for many different bare transition metal clusters have been determined in the gas-phase. [18][19][20][21][22] Whetten et al have studied the reactions of Fe and Nb clusters with H 2 and D 2 , respectively, and have suggested that the relative reaction rates track closely with small variations in cluster ionization thresholds. 23,24 The reactivity of most small alkanes with gas-phase transition metal atoms and clusters is quite difficult to measure due to the nonreactive nature of these species, excluding uncontrolled rapid oxidation.…”

Calculation of photoionization cross sections of Na2–8 and K2–8 clusters

“…Electronic structure calculations [5][6][7][8] treating the valence electrons as non-localized electrons within the jellium model have shown that these magic numbers correspond to spherical shell closings. Today abundant experimental data on electron shell structure and magic numbers are available, especially for alkali element clusters [4,[11][12][13][14][15][16][17] and other freeelectron-like metal clusters such as Cu, [18][19][20][21][22], Agn [23] and np elements such as Aln [20,24,25]. These have been interpreted as the shell closings of ellipsoidally deformed clusters [9] using the Nilsson model [10], which was originally developed in nuclear physics.…”