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Clusters of argon, krypton, and xenon are grown in a free jet and ionized by electron impact. The size of these clusters, (Rg)+n, extends up to n[bar_over_tilde:_approx._equal_to]1000. Individual cluster sizes are mass resolved up to n[bar_over_tilde:_approx._equal_to]570 in the case of Ar+n. The well known, but puzzling differences in the size distributions of Kr and Xe clusters disappear beyond n[bar_over_tilde:_approx._equal_to]130, while those between Ar and Xe disappear beyond n[bar_over_tilde:_approx._equal_to]220. The most pronounced ‘‘magic numbers’’ in the distributions of large cluster ions occur at n=147 (148 for Ar), 309, and 561, in striking agreement with the number of atoms required to build icosahedral clusters with 3, 4, and 5 complete coordination shells, respectively. Closure of the 6th icosahedral coordination shell is indicated by another strong intensity drop at n[bar_over_tilde:_approx._equal_to]923 in the unresolved part of the spectra. Several additional intensity extrema are observed between major shell closures. A simple structural model, assuming an icosahedral core decorated by the additional atoms, accounts for these anomalies reasonably well up to n=561. [ABSTRACT FROM AUTHOR]

Fully resolved mass spectra of carbon monoxide clusters have been recorded in the size range n≦320. Intensity anomalies in these spectra beyond n=135 are strikingly similar to those being observed in krypton and xenon spectra. Particularly pronounced intensity drops occur at n=147 and 309. For the first time, these data provide evidence for icosahedral structure in large molecular cluster ions. Concerning doubly charged CO clusters, their lower size limit has been measured to be n=98. [ABSTRACT FROM AUTHOR]

In extracts from Phaseolus vulgaris seeds an enzyme has been found which transfers the galactosyl moiety of galactinol to raffinose giving rise to stachyose and myo-inositol. Two tests to measure the enzyme activity are described. The reaction is reversible. An equilibrium constant of approximately 4 has been determined for [stachyose][myo-inositol]⁄[raffmose][galactinol]. The enzyme catalyzes exchange reactions between galactinol and myo-[14C]inositol and between stachyose and [14C]raffinose. Specifically labeled galactinol and stachyose can be prepared in this way. The Km values for galactinol and for the two best galactosyl acceptors, raffmose and melibiose, have been measured. Besides the galactinol: raffinose-6-galactosyl transferase the extract of the seeds also contains an &alph;-galactosidase, which separates from the transferase during the purification. The transferase is strongly inhibited by p-chloromercuribenzoate. Ripening seeds contain an enzyme which catalyzes the reaction UDP-galactose + myo-inositol → galactinol + UDP. However, no direct transfer of galactose from UDP-galactose to raffinose has been observed. The physiological importance of the results is discussed. [ABSTRACT FROM AUTHOR]

Silver clusters are generated by standard laser vaporization technique and ionized via multiphoton ionization. Time-of-flight mass spectrometry reveals singly, doubly and triply charged clusters, Ag ( z=1,2,3). The spectra show, for all charge states, intensity variations, indicating enhanced stabilities for cluster sizes with closed electronic configurations in accord with the spherical jellium model. [ABSTRACT FROM AUTHOR]

Metastable decay of (N), formed in a supersonic jet and ionized by electron impact, has been analyzed for n≤50. The probability for decay of (N) into (N), plotted versus x, exhibits pronounced oscillations. The 'period' of these oscillations increases with increasing precursor size n, but converges to an average value of approximately 4.7 beyond n=25. [ABSTRACT FROM AUTHOR]

The superior stability of closed-shell icosahedral structures is evident from size distributions of argon, krypton and xenon cluster ions in the size range 100≲ n≲1000. [ABSTRACT FROM AUTHOR]

This is a first report concerning the thermionic emission of electrons from hot metal clusters. Tungsten clusters were exposed to a 10 ns laser pulse, and the delayed emission of electrons from the clusters was recorded as a function of time after the excitation. A large yield of W cluster ions, which were born as late as microseconds after the laser pulse, has been detected for n>4. Tungsten cluster ions created via thermionic emission show no measurable metastable decay during the flight time in the mass spectrometer. This indicates that they are colder than expected, if evaporative cooling after prompt ionization would prevail. [ABSTRACT FROM AUTHOR]