In all liquids, the free-ion yield increases with the external electric field E. An important feature of the Onsager (1938) theory is that the slope-to-intercept ratio (S/I) of the linear increase of free-ion yield with the field at small values of E is given by e3/2efeB2T2, where is the dielectric constant of the medium, T is its absolute temperature, and e is the magnitude of electronic charge. Remarkably S/I is independent of the electron thermalization distance distribution or other features of electron dynamics in fact, it is free of adjustable parameters. The theoretical value of S/I can be calculated accurately with a known value of the dielectric constant it has been well verified experimentally in a number of liquids, some at different temperatures (Hummel and Allen, 1967 Dodelet et al, 1972 Terlecki and Fiutak, 1972). [Pg.305]

Unlike the oxymercuration of acyclic olefins, oxymercuration of bicyclic olefins often gives jy -addition products. Norbornenes 93, for example, show exclusive fvo-oxymercuration. In this reaction, the ratio between the isomers depends on the nature of the fvo-substituent (R1) and tro/o-substituent (R2) (Equation (36)). The presence of electron-withdrawing fvo-substituents always leads to a much greater selectivity in favor of 94a-d over 95a-d.116 117 As indicated by extensive theoretical calculations, the charge distribution in the transition states governs the selectivity of these reactions.118 [Pg.435]

There is another aspect that makes measurements of transition probabilities very attractive with regard to a more detailed knowledge of molecular structure. Transition probabilities derived from computed wave functions of upper and lower states are much more sensitive to approximation errors in these functions than are the energies of these states. Experimentally determined transition probabilities are therefore well suited to test the validity of calculated approximate wave functions. A comparison with computed probabilities allows theoretical models of electronic charge distributions in excited molecular states to be improved [2.19,2.20]. [Pg.26]

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