Tritium recoil studies

Annealing st idies are perhaps of minor interest in carbon and tritium recoil since they yield little information about the chemical reactions which are occurring. The studies are also limited to solids. They do. however, have a direct and significant bearing on the nature of the solid state and on the physical aspects of the recoil process. 

B. Excitation-Decomposition in Svbstitution Hoflf and Rowland (1957), in studying the reactions of tritium recoils with methanol, ethanol, and acetone, suggested the same reactions in order to account for most of their observed products in the liquid phase. In addition, they postulated an excitation-decomposition reaction as given in eqs. (10) and (11) in order to explain the formation of labeled acetaldehyde from ethanol. 

With fluoro-compounds, there has been work on the radiolysis of fluorinated methanes , hexafluoroethane , tetrafluoroethylene - , fluorobenzene , cyclic fluorocarbons , trifluoroiodomethane - - , and perfluorocar-bons . Most studies have involved the use of y-radiation, but Yi-Noo Tang and Rowland have discussed the recoil tritium-excitation of ethyl fluoride (and ethyl chloride), providing evidence for 1,2-HX elimination. 

Radiolysis studies on chloro-compounds have included those on chlorinated methanes - - - , 1,2-dichloroethane , chlorotriphenylmethane - , chloroolefins , benzyl chloride - , a-chlorotoluene , and chloroacetic acids . Recoil tritium reactions with dichloromethane and chloroethane have also been reported. 

The gas-phase reactions of recoil tritium atoms (generated in the He(n,p) H nuclear reaction) with gaseous arsine, AsHj, at high pressure has been studied in mixtures either with or without the scavenger ethylene. In the absence of scavenger about 67.3% of the tritium has been found as H H(HT) and about 31.8% as ASH2T. 

Carbenes and Silylenes. Carbenes such as CTF and CTCl were formed in recoil tritium systems (35-39), while carbenes such as CH F, CH C1, and CF F were formed in recoil halogen atom studies (40-44). Among them the truly unusual ones are the monofluorocarbenes, CTF and CH F, because their chemical interactions were first studied by these nuclear recoil methods (36 37y40y41,45). The details of such studies will be described in a later section. 

Surface ionization studies of Reaction 1 necessarily involved the detection of the much heavier product, KBr, which was constrained by the conservation of momentum to scatter close to the center of mass (c.m.). In this case, the small recoil velocity of the product KBr from the c.m. is masked by the spread of the c.m. velocity vectors arising from the distribution of parent beam velocities. Thus, it becomes diflBcult to extract any information about the motion of the KBr relative to the c.m., which would provide the desired description of the mechanism and energetics of the reaction (9). High velocity resolution experiments have since been done by Bernstein and coworkers (10,11), but the studies of Reactions 2 and 3 by Martin and Kinsey (8) were the first to provide some information on the dynamics of these reactions from a measurement of product distributions. In these experiments tritium labeling allowed radioisotope... 

E. Dovble-Bond Addition Reactions Reactions of recoil tritium atoms in alkenes have been studied and have brought to light an additional reaction type. The energetic tritium atom can add to the double bond. Urch and Wolfgang (1959) have substantiated this hot addition by studying scavenger and moderator effects in alkenes. Decomposition of the hot radical once formed follows a pattern similar to that of the decomposition of thermally excited free radicals, namely... 

A detailed study of the products and intramolecular tritium distribution in the parent, when liquid phenylacetic acid was recoil-labeled, was made by Elatrash and Johnson (1961). They concluded that distribution in the excited parent was essentially random with little or no steric elfect being involved. They explain the exceptionally low activity observed in the methylene group of the labeled parent by suggesting that tritium substitution at the methylene position leads to an excited intermediate whose probability of de-excitation to labeled parent is considerably lower than when other positions in the molecule undergo substitution consequently a greater number of the methylene-substitution intermediates fragment rather than stabilize. The mechanistic emphasis here is on the excitation in the intermediate. 

Similar experiments nsing various organic substances give mean excitation energy in recoil tritium reaction. O Table 24.4 lists selected cases for such studies (Tominaga and Tachikawa 1981). Note that the recoil reaction of for fluorine gives the largest values around 10 eV. 

A method for preparing tritium-labelled oligosaccharides of hyaluronic acid has used the Wilzbach recoil technique the tritiated oligosaccharides are of potential use in studies of the mechanism of hyaluronidases. A four-fold helical form of hyaluronic acid has been detected using the data from fibre-... 

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