Magic numbers in transition metal (Fe, Ti, Zr, Nb, and Ta) clusters observed by time-of-flight mass spectrometry

Abstract

We have measured time-of-flight (TOF) mass spectra of transition metal free clusters, TMn (TM=Fe, Ti, Zr, Nb, and Ta and n is the number of atoms per cluster), produced by a laser vaporization source. The size resolved TOF intensities at n=7, 13, 15 are much higher than those at the neighboring n values for all TMn. Such specific n values are assigned to the magic numbers of these transition metal clusters and can be related to pentagonal bipyramid, icosahedron, and bcc structure units. The other magic numbers are observed for larger TMn: n=19 and 23 for Fe, n=19 and 25 for Ti, being attributable to the polyicosahedron. The TOF spectra of Nb and Ta clusters are similar to each other and display the common magic number of n=22.

Ion-pair evaporation from ionic liquid clusters

“…No unusually volatile or involatile clusters were apparent in negative mode. Unlike cluster abundance measured by MS alone [14], here the measured abundance of each cluster is directly related to the cluster's evaporation rate relative to its neighbors.…”

Experimental vibrational spectra of gas-phase tantalum cluster cations

“…In fact, it has been reported to also be a magic peak in the mass spectra. 21 Recently, capped cubic structures have been proposed for 13-atom clusters of the later transition metals. [41][42][43] Supposing that only one isomer is present in the molecular beam, a strictly symmetric icosahedral structure can be ruled out for Ta + 13 , since it would only show two infraredactive(T 1u ) bands.…”

“…Magic numbers of tantalum clusters have been reported in time-of-flight (TOF) mass spectra, 21 even though intensities of transition-metal clusters in mass spectra normally show little size dependence. The reactivity of neutral Ta clusters with hydrocarbons and N 2 has been studied.…”

Magic number behavior for heat capacities of medium-sized classical Lennard-Jones clusters

“…[14][15][16][17] Computer simulations of clusters have revealed a wide diversity of fundamental behavior that is highly sensitive to many factors, such as the cluster aggregate size N , the potential used to model the intermolecular interactions, and even the simulation method itself. The Lennard-Jones (LJ) potential is the most commonly used model potential for computer simulations of cluster properties, and it is especially useful for modeling rare gas clusters.…”

“…Because of their high proportion of surface atoms, many clusters have physical properties that typically exhibit a very irregular dependence on their aggregate size, with certain sizes standing out in particular. For example, the mass spectra of clusters typically exhibit especially abundant sizes that often reflect particularly stable structures, specially reactive clusters, or closed electronic shells, [12][13][14]17 These "magic number" sizes have been of great theoretical interest, [11][12][13] and much work has been done in relating magic number sequences to cluster structure in terms of "soft" sphere packings, since many magic number sizes in LJ clusters such as N = 13, 19, 55, and 147 correspond to compact structures that are especially stable. 1, 7 Many cluster properties obtained from simulation studies such as binding energies, root mean square (rms) bond length fluctuations and heat capacities also show very irregular dependencies on the cluster size that mostly correspond to their usual magic number sequences.…”