Itsuo Katakuse

Mass distributions of copper, silver and gold clusters and electronic shell structure

Abstract Mass distribution of copper (Cu)n+, silver (Ag)n+ and gold (Au)n+ clusters were investigated up to cluster size n = 250. The clusters were produced by bombardment of 10 keV Xe ions and were analyzed using a sector-type mass spectrometer. The mass distributions for these metal clusters were similar. The ion intensity of clusters decreased with increasing cluster size, n. Superimposed on this general decrease, two types of anomalies were observed. One anomaly was a regular variation of ion intensity between odd and even numbers of n, where the intensity of odd-n clusters was greater than that of even-n. The other anomaly was a discontinuous variation of cluster ion intensity at peculiar numbers of n. These numbers were 3, 9, 21, 35, 41, 59, 93, 139 and ∼ 200. This behavior can be explained by a one-electron shell model in which electrons are bound in a spherically symmetric potential well.

Mass distributions of negative cluster ions of copper, silver, and gold

Abstract Mass distributions of negative cluster ions of copper (Cu) n − , silver (Ag) n − , and gold (Au) n − obtained by the bombardment of metal sheets with Xe ions were investigated up to cluster size n = 250 and were compared with those of the positive cluster ions. The mass spectra were obtained under the same conditions as previously employed to study positive cluster ions and the behaviour of the mass distributions of the negative cluster ions were very similar to those of the positive cluster ions. The ion intensity of the clusters decreased with increasing cluster size, n , and two types of anomaly were observed. One was a regular variation of the ion intensity between odd and even values of n , where the intensity of odd- n clusters was greater than that of even- n , which is explained by pairing of the electrons. The other anomaly was a discontinuous variation of ion intensity at specific numbers n = 1, 7, 17, 19, 33, 39, 57, 91, 137, and 197. In the mass spectra of positive cluster ions, these were 3, 9, 19, 21, 35, 41, 59, 93, 139, and 199. It is confirmed from this intensity behaviour that a one-electron shell model can be applied to explain the stability of those metal clusters in which s valence electrons are bound in a spherically symmetric potential well.

Structural analysis of human hemoglobin variants with field desorption mass spectrometry

Tryptic hydrolyzates of normal and abnormal human globin chains were analyzed with mass spectrometry, using field desorption ionization technique. All the peptides, including core peptides, were detected as protonated molecular ions in field desorption mass spectra. Since the technique makes it possible to determine the mass number of each peptide, it is very useful for structural analysis of human hemoglobin variants, even those with electrophoretically and chromatographically silent mutations.

Correlation between mass distributions of zinc, cadmium clusters and electronic shell structure

Mass distributions of zinc (Zn)n+ and cadmium (Cd)n+ clusters have been investigated up to the cluster size n = 75. The clusters produced by the bombardment of the metals by 10 keV Xe ions have been analyzed using a single focusing mass spectrometer. The mass distributions for these metal clusters are quite similar. The ion intensity of clusters decreases with an increase of n. Superimposed on this general decrease, abundant ion currents are observed for clusters with n = 10, 18, 20, 28, 30, 32, 35, 40, 41, 46, 54, 57, 60 and 69. These numbers can be explained by a shell-closing effect of s-valence electrons which are bound in a spherically symmetric potential well of the cluster. The most probable potential is the finite square well potential with round edges.

A new time-of-flight mass spectrometer

Abstract A new time-of-flight mass spectrometer consisting of four 269° electric sector fields was constructed. Triple isochronous focusing and triple space focusing were achieved simultaneously by the symmetrical arrangement of four sector fields. The flight length of the system is 1.727 m, even though the diameter of the vacuum chamber is 41 cm. TOF mass spectra were taken by a pulsed electron impact ion source (FWHM 15 ns). The peak width (FWHM) of 18 ns at m/z = 132 was obtained.

Fission-like dissociation of doubly charged silver clusters

The dissociation patterns of doubly charged silver clusters (Ag)2+n to singly charged clusters (Ag)+m have been investigated. They were produced by the Xe+ ion bombardment of a silver sheet and were mass-analyzed using a double focusing mass spectrometer; the resulting ion intensity was < 1% of that of singly charged clusters. The daughter ions, the size of which is larger than n/2, were detected without the interface from those decaying from singly charged clusters by lowering the acceleration voltage below the normal value. The decomposition probabilities as a function fo m-value had a tendency to increase as the difference between m-values and n/2 decreased. Superimposed on the increase, an enhanced ion intensity at certain m-values and an odd-even alternation were observed in which the intensity of odd-m clusters was larger than that of even-m.

Mass distribution of peptide molecular ions in the secondary ionization process

Abstract In the mass spectra of peptides obtained by positive SIMS (secondary ion mass spectrometry) using a liquid matrix, it was observed that molecular ions having the monoisotopic mass other than M + 1 were produced with significant intensities especially in the high mass region ( m/z >1000). The products were analyzed into unit mass in the mass region near the molecular ion and the precise intensity ratios of the mass peaks were obtained by using a pulse counting technique. Subtracting the effect of mass distribution caused by the presence of isotopic ions, the abundances of the ions other than M + 1 were estimated. The distribution obtained showed a close correlation with the structure as well as the weight of molecule.

Structural analysis of human hemoglobin variants by mass spectrometry

Abstract FD and FAB mass spectrometries were applied to structural analysis of human hemoglobin variants. All peptides were identified in the FD mass spectrum of the tryptic peptide mixture of β-globin. The method permits us to detect the abnormal peptide containing amino acid substitution, and moreover to determine the type and position of substitution without further conventional amino acid analysis.

Metastable decay of cesium iodide cluster ions

Abstract Metastable decay of the cluster ions [(CsI) n Cs] + with n = 7 to 38 was investigated by using a double focusing mass spectrometer of normal geometry. The energy distributions of the cluster ions, when entering the mass spectrometer, vary in a different manner with n values, due to metastable decay. It is confirmed that the n = 13 and 22 cluster ions are more stable to metastable decay than others and seem to be anchor points in metastable decay chains of the higher n cluster ions.

A new mass spectrometer at Osaka University

Abstract A new double-focusing mass spectrometer for heavy molecule analysis has been constructed at Osaka University. The instrument consists of a field arrangement of two quadrupoles, a 41° homogeneous magnetic field (rm = 125 cm), a third quadrupole, and a 90° cylindrical electric field (re = 90 cm). The quadrupoles are used as the defocusing mode in the horizontal (x) direction and as the focusing mode in the vertical (y) direction, so that the beam profile in the magnet gap is very wide in the x direction and narrow in the y direction. As a result, two advantages are obtained simultaneously; one is a high beam transmission through a narrow gap magnet (2 cm) and the other a small image magnification (0.2) to increase both sensitivity and resolution. A mass resolution of 10 000 (90% valley) was obtained with an object slit of 250 μm. Mass spectra of CsI up to m/z = 50 000 were obtained at 5 kV acceleration under the mass resolution of 600.