Cyclotron experiments, early

Considerable interest in the subject of C-H bond activation at transition-metal centers has developed in the past several years (2), stimulated by the observation that even saturated hydrocarbons can react with little or no activation energy under appropriate conditions. Interestingly, gas phase studies of the reactions of saturated hydrocarbons at transition-metal centers were reported as early as 1973 (3). More recently, ion cyclotron resonance and ion beam experiments have provided many examples of the activation of both C-H and C-C bonds of alkanes by transition-metal ions in the gas phase (4). These gas phase studies have provided a plethora of highly speculative reaction mechanisms. Conventional mechanistic probes, such as isotopic labeling, have served mainly to indicate the complexity of "simple" processes such as the dehydrogenation of alkanes (5). More sophisticated techniques, such as multiphoton infrared laser activation (6) and the determination of kinetic energy release distributions (7), have revealed important features of the potential energy surfaces associated with the reactions of small molecules at transition metal centers. 

The key experiment which showed that plutonium-239 undergoes fission when bombarded by slow neutrons was performed with a cyclotron at Berkeley early in 1941. 

Mendelevium — (Dmitri Mendeleev [1834-1907]), Md at. wt. (258) at. no. 101 m.p. 827°C valence +2, +3. Mendelevium, the ninth transuranium element of the actinide series to be discovered, was first identified by Ghiorso, Harvey, Choppin, Thompson, and Seaborg early in 1955 as a result of the bombardment of the isotope Es with helium ions in the Berkeley 60-inch cyclotron. The isotope produced was Md, which has a half-life of 78 min. This first identification was notable in that Md was synthesized on a one-atom-at-a-time basis. Nineteen isotopes and isomers are now recognized. Md has a half-life of 51.5 days. This isotope has been produced by the bombardment of an isotope of einsteinium with ions of helium. It now appears possible that eventually enough Md can be made so that some of its physical properties can be determined. Md has been used to elucidate some of the chemical properties of mendelevium in aqueous solution. Experiments seem to show that the element possesses a moderately stable dipositive (II) oxidation state in addition to the tripositive (III) oxidation state, which is characteristic of actinide elements. 

Several earher claims for the detection of naturally occurring element 61 were eventually refuted. Among the names in the course of the early claims were illinium (after Illinois), florentium (afler Horence, Italy), and cyclonium (after the use of the cyclotron accelerator). Even the last claim was incorrect, although the eventual discovery was indeed made in a particle accelerator experiment. 

The ion-molecule reactions of collisionally relaxed NH2 with typical representatives of organic compounds in the gas phase at ambient temperature are compiled in Table 22. The anions were analyzed by mass spectrometry in early experiments and later by Fourier transform (ion cyclotron resonance) mass spectrometry. More recent investigations usually apply the flowing afterglow technique or its offspring, the selected-ion flow tube (SIFT) technique. These methods allow the identification of anions only the other products have to be deduced from the mass balance. Rate constants were determined by the flowing afterglow and the SIFT techniques. The products frequently form by proton abstraction which may be followed by elimination or by nucleophilic substitution. Reaction enthalpies and... 

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