Opacity function models

The influence of chemical reactions on elastic scattering has been extensively studied in the past. Nearly all treatments are based on the optical model (for a review see Ross and Green, 1970). Both the imaginary part of the potential (here assumed to be local) and the opacity function have been parameterized (Mariott and Micha, 1969 Harris and Wilson, 1971 and references cited therein). For a study of the total cross section see Diiren et al. (1972), A semiclassical study of a bimolecular exchange reaction where the three atoms are constrained to move on a straight line but the whole system is free to rotate in three dimensions, predicts a new kind of rainbow (Connor and Child, 1970),... 

In our calculations for F + we are always in an energy range to which Eq. 6 applies. Finally, the orientation-averaged opacity function P3(biBp) for the ADLOC model is given by [2,3,10]... 

N. Peripheral collisions. Reactions such as Cl + CH4 or H + HCl may be more likely to occur at higher impact parameters. This is because reaction requires the three atoms. Cl—H—C or H—H—Cl, to be nearly in a collinear configuration and this is easier to achieve for an off-center collision. Make a model where the center of mass of HCl is on the Cl atom. Place the bound H atom on a sphere about the center. Assume that reaction occurs when H—H—Cl is in a collinear configuration. Hence compute the opacity function vs. b [adapted from P. M. Aker and J. I Valentini, Is. J Chem. 30, 157 (1990)]. 

The age at which Li depletion occurs increases with decreasing mass (and Li-burning temperatures are never reached for M < 0.06 M0). As luminosity, L oc M2 for PMS stars, the luminosity at which complete Li depletion takes place is therefore a sensitive function of age between about 10 and 200 Myr [6]. This relationship depends little on ingredients of the PMS models such as the treatments of convection and interior radiative opacities because the stars are... 

Bound-bound absorption is very important in stellar atmospheres and stellar envelopes, where many millions of lines, particularly from iron-group elements, have been shown to have a profound influence on stellar models. The frequencies which dominate the opacity must correspond roughly to the peak of the Planck function, i.e. vmax/T = b (Wien s law again). Most atomic transitions have wavelengths longer than 100 A, so for T > 5 x 106K, bound-bound absorption becomes less important. 

Numerical models have been relatively successful in describing the physical conditions in the solar interior. The models generally assume that the Sun consists of mass fractions of hydrogen, X, helium, T, and heavier elements, Z. The fraction Z lumps together all elements from lithium to uranium Z is often taken to be 0.02 in the models. Since X + Y + Z = I only one free parameter is left to characterize solar bulk composition. The models also assume spherical symmetry and hydrostatic equilibrium. Except for a small zone near the visible surface, temperatures inside the Sun are so high that atoms are fully ionized. The equation of state, the radiative opacity, and the energy production rates, all needed in the models as functions of temperature and density, can then be found from stellar interior and nuclear theories. Of course, matters are more complicated readers interested in stellar models may wish to consult books on that subject, for example, the one by Clayton (1968). 

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