No abstract

The most commonly applied model for correlating reaction rate data is the power function rate equation, which requires careful data analysis for estimation of the reaction order. The authors present a method for the analysis of

No abstract

Analytic expressions are presented which may be used to compute the sputter-erosion yield from any unimolecular gravitationally bound gas by any atomic charged particle of any energy. A calculation of solar wind proton and alpha particle induced erosion of the CO2 atmosphere of Mars predicts molecular sputtering yields S•, • 0.029 and S,• • 0.21. These numbers are comparable to the results of earlier Monte Carlo simulations. An expression for the emission yield of energetic molecular fragments produced in primary knock-on events is also given in closed form. Such fragment emission is of secondary importance for mass loss compared to the molecular yield itself. Erosion by radiation belt protons of a hypothetical thin 02 atmosphere associated with the Jovian satellite Ganymede is considered. Molecular sputtering yields for proton energies at 1 keV and 1 MeV are 0.115 and 6.4 x 10 -4, respectively. The yield at the lower energy can have significant effects on atmospheric equilibrium should keV proton fluxes equal or exceed about 108 cm -2 s -l.

Elemental and isotopic mass fractionation in both binary and multicomponent media are investigated within the framework of the familiar collision-cascade model for sputtering. Some of the most salient features of the phenomenon are explicable on this basis. It is found that the partitioning of beam-deposited energy among the various target components can account for differentiations in the secondary recoil fluxes only on the order of one part per thousand, indicating the importance of the surface potentials when large enrichment effects occur. A mechanism governing the translation of internal recoil fluxes into external sputtered fluxes is proposed in order to account for isotopic fractionation, for which the surface binding effects are assumed to be negligible. The predicted initial fractionations are δf(40Ca : 44Ca) =33 parts per thousand in the calcium-containing mineral plagioclase and δf(40Ca : 44Ca) =24 parts per thousand in CaF2, in reasonable agreement with recent data on isotopic fractionation.

No abstract

No abstract

No abstract