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Figure 1. Part of the NH-CJH region of the 300-MHz NOESY spec-trum (2K X 2K data matrix) of the decapeptide LHRH. The two framed regions 1 and 2 showing severe overlaps are also plotted on expanded scales. The corresponding regions from the NOESY TR spectrum (700 f, samples zero filled to 2K X 2K) exhibiting homonuclear decoupling in the uq dimension are shown in the frames V and 2'. No undesired cross peaks (see text) appeared in the NH-CJH region so suppression10 was unnecessary. N = 4 (see text) was sufficient in this experiment since the Ca protons can have at maximum three coupling partners, leading to the seven-step cycle ¡0°;0.

Buckminsterfullerene, c60, was prepared in gram quantities by contact-arc vaporization of a graphite rod in a 100-Torr atinospherc of helium. followed by extraction of the resultant graphitic soot with toluene. The dominance of C , in this extract was verified by mass, FTIR. and NMR spectroscopy. The molecule was successfully hydrogenated to C6,H,, via a Birch reduction and dehydrogenated back to bare c 6 0 by treatment with DDQ reagent. Cyclic voltammetry of C60 in methylene chloride rcvcaled highly reversible formation of at least two stable anionic forms of c 6 0 in solution. A broad new class of thcsc fulleride and fulleronium ions is anticipated, both with the internal cavity empty and with any one of a large number of elcmcnts inside, thus providing a means of fine-tuning the chemical, optical, and redox properties.

The laser-induced fragmentation behavior of positive carbon cluster ions has been investigated by tandem time-of-flight techniques for the jet-cooled clusters up to 80 atoms in size. Two distinct photophysical regimes were found. The first applies to clusters with 34 atoms or more, all of which dissociate to produce even numbered fragments. Large even clusters fragment by the loss of the high energy species C2, odd ones lose a C atom. The second regime applies to clusters composed of 31 or less atoms, all of which fragment by the loss of C3. These two regimes are sharply separated by C+32 which fragments to produce small cluster ions in the 10–19 atom size range. Fragmentation of the large clusters occurs on a microsecond or faster time scale only at very high levels of excitation (>12.8 eV). These photophysical results are interpreted as consequences of the large even clusters having edgeless, spheroidal cage structures while the small ones have linear chain or ring structures.

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A new fast flow device for the study of metal cluster reactions in the gas phase is described and characterized. The new device utilizes metal clusters made by laser vaporization of an appropriate metal target mounted in the throat of a supersonic nozzle which exhausts into a fast-flow reaction tube. Reactants are injected into the flowing helium–metal cluster mixture at a point in the flow tube where shock waves have reheated the gas to roughly 320 K. Turbulence in the wake of these shock waves produces efficient mixing of the reactants. Measurement of the flow properties of this reaction tube indicate a residence time of 150–200 μs with an average density of helium buffer gas equivalent to 50–100 Torr at room temperature. Subsequent free expansion of this reaction mixture into a large vacuum chamber produces a supersonic beam with extensive cooling of the various constituents in the mixture (pyrazine was measured to be rotationally cooled to 10 K). The new cluster reaction device is, therefore, an excellent source for future studies of the jet-cooled metal cluster reaction products themselves.