Recoil chemistry studies

Study of the recoil chemistry of organometallic compounds for its own sake, began really in 1955 with the publication of a study (56) by Mad-dock and Sutin on neutron activation of triphenylarsene. Since this time, most of the published work has been focussed on those radioactive atoms which did not permanently escape their ligands. Thus, in one way or another, they end up in molecular form. It is with these that this review is largely concerned. 

It is likely that the answers to these questions will come only from more selective and sophisticated experiments than have been done hitherto, although some useful directions have been established. The use of high-sensitivity electron spin resonance for the study in situ of anticipated radical species will likely be possible, if the background signals from other radiation-produced species are not too intense. Studies of the chemistry of implanted atoms and ions in solid organometallic substrates will make it possible to start with totally unbound atoms which suffer no Auger ionization and thus to simulate the extreme of the total recoil. Careful studies of the thermal annealing effects, especially in the presence of reactive atmospheres, will... 

Recoil Chemistry and Mechanistic Studies with Polyvalent Atoms... 

While such a reaction is in principle possible, it is expected to occur with very low eflBciency. In the recoil chemistry of polyvalent atoms, chemically stable reaction products are likely to be formed in multistep reaction sequences rather than in single reactive collisions. This implies the formation of reactive intermediates, which is the feature that most clearly distinguishes the study of polyvalent atoms from the investigation of monovalent atoms. 

The most important mechanistic clue for any chemical reaction is the structure of the reaction products, and a great strength of the recoil technique is that there is no more convenient or effective way to determine what products are formed from a polyvalent atom and a chosen reaction substrate than by examining its recoil chemistry. The harshness of the conditions required to liberate polyvalent atoms chemically severely limits the study of their reactions by other methods (vide infra). 

These examples point to the symbiotic relationship between polyvalent atom recoil chemistry and the study of chemically generated reactive intermediates. Hot atom experiments identify products that suggest the intermediacy and delineate the reactivity of exotic species such as cycloproplyidene, methyne, and silylene. Thus, hot atom experiments have stimulated the search for other ways of generating these species, and in turn these chemical experiments can help interpret the hot atom experiments. 

Early in the study of silicon atom recoil chemistry, ethylene was used as a scavenger to diflFerentiate between silyl radicals, SiHs, and silylene, SiH2, as the intermediate responsible for the formation of silane and disilane in phosphine-silane systems (21). 

CASPAR Recoil Chemistry arid Mechanistic Studies... 

Many kinds of metals have been studied by evaporation-cocondensation (120y 124-126) but thus far, little recoil chemistry has been carried out. The mechanistic interest and commercial importance of olefin metathesis reactions (127) suggests... 

A natural area of interest for chemists studying high-energy polyvalent atoms is cosmochemistry. With growing indications that high-energy reactions of carbon and silicon atoms are important processes in the formation of interstellar grains, it can be predicted with confidence that the recoil chemistry of polyvalent atoms will claim the attention of cosmochemists and laboratory astrophysicists (129-133). 

The recoil chemistry of carbon-11 in liquid C5-C7 hydrocarbons has been investigated by Clark The recoil atoms have been produced in the (y,n) reaction. The study of the product yields of ethane, ethylene and acetylene (as well as of methane) from different target molecules has been the main concern in this work. Iodine affected the yields of all the volatile products except acetylene. Acetylene-the principal products in all the hydrocarbons investigated, is produced in hot reactions with naked atoms. Insertion of recoil fragments into C—H and C=C bonds leads to various C-labelled hydrocarbons. 

Kirbach, U.W., Gregorich, K., Ninov, V., Lee, D.M., Patin, J.B., Shaughnessy, D.A., Strellis, D.A., Wilk, P.A., Hoffman, D.C., Nitsche, H. The recoil product transfer chamber (RTC) A new interface for heavy element chemistry studies at the Berkeley gas-filled separator. In Nuclear Science Division Annual Report 1999. Lawrence Berkeley National Laboratory, Berkeley, (1999)... 

Physical Methods Used to Study Recoil Chemistry... 

The recoil chemistry of Cd phthalocyanine has been studied by following the behaviour of the In daughter product. The argument is that no bond rupture occurs in the beta decay, and all observed effects are due to the (n,y) reaction during the production of Cd. This is contrary to general experience in p decay studies (see Section 7). The evidence is that cadmium phthalocyanine, which is ionic, anneals even at 20 C, in contrast to crystals of the copper and zinc complexes. A detailed analysis of the annealing kinetics is given. ... 

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