Publication costs assisted by the French Atomic Energy CommissionThe formation of CI2by pulse radiolysis and its subsequent disappearance, in the presence and absence of N20, have been studied with neutral LiCl solutions of concentrations up to 14 M. In deaerated solutions, the yield with respect to the total absorbed dose shows a maximum at about 9 M, where G(Cl2~) = 3.4, and decreases at higher concentrations. This would seem to indicate that the direct effect on the Clions gives rise to almost no CI2-, while the yield of primary species responsible for its formation (H20 radiolysis) would appear to be about 4.7.

The dynamical evolution of an intense ultrashort sub-10-fs two-cycle optical pulse is considered as it propagates through a transparent third-order dielectric medium characterized by three resonance lines and a finite sub-fs relaxation time of the electronic nonlinearity. Numerical integration of the full Maxwell's equations incorporating triple-resonance Lorentz linear dispersion and Debye nonlinear dispersion, for a linearly polarized electromagnetic pulse centered at lambda(0)=1.24 microm in the normal dispersion region near the zero dispersion wavelength, shows the formation of shocks occurring on the optical cycle due to the generation of optical harmonics. The finite relaxation time of the nonlinear electronic response (sub-fs time scale) (i) slows down the steepening rate of the optical cycle; (ii) does not limit the generation of strongly phase matched optical harmonics, and consequently the development of infinitely sharp edges on the optical cycle producing its breaking when linear dispersion is not included; (iii) reduces the production of phase matched harmonics and consequently the sharpening of the jumps when dispersion is present, compared to the case of an instantaneous nonlinear response; and (iv) reduces the harmonic spectrum spreading and modulation at later times on the appearance of self-steepening of the electric field envelope.

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The pulse radiolysis of cold ethanol near its freezing point shows 'partly solvated' states of the electron with transient spectra whose maxima vary with time. It is shown that the determination of the solvation times of the electron can depend strongly on the wavelength considered; thus an explanation could be given for the different values obtained by Chase and Hunt at λ = 1300 and λ = 1050 nm.

Publication costs assisted by Commissariat á I'Energie AtomiqueThe effect of the dielectric constant of the solvent on the reactivity of the solvated electron formed by pulse radiolysis has been studied in water-ethanol mixtures. It was found that the rate constant k(es~+ NOb-) diminishes with decreasing water concentration whereas ¿(es~+ Zn2+) increases in going from pure water to 60% by weight ethanol. On the other hand, k(es~+ H+) is almost invariant with the solvent composition, from pure water to 99% by weight ethanol. From measurements of the rate constant of the very fast reaction es~+ C6HSN02 we have estimated the diffusion coefficient of the solvated electron in water-ethanol mixtures. Using the appropriate equations with the values of the diffusion coefficient of es-thus determined we have shown that it is possible to correlate the rate constants of the reactions between solvated electrons and ions with the macroscopic dielectric constant of the medium. The distance at which reaction takes place is, in each case, approximately equal to the sum of the individual ionic radii.