![]() The Y, B, and V$sub 12$(R) diabatic potentials have been obtained by judicious extension (and manipulation) of the spectroscopically derived B and B' adiabats. The possibility of translational-electronic energy transfer arises from the $sup 3$Pi$sub 0$+ potential curve crossing at E=0.25 eV, responsible for the well-known IBr predissociation. Two-state, close-coupled quantal computations of the elastic and inelastic scattering of ground-state I atoms by ground-state Br and spin-orbit excited Br* atoms have been carried out over a range of total energies E from 0.01 to 0.94 eV. The Landau-Zener formula is shown to be quite satisfactory for the present application. It is shown that the inner region is dominant at the higher energies and that the outer region is dominant at the lower energies. The outer-region cross section is first obtained from the Landau-Zener formula and then computed directly from the adiabatic close coupling of states 650 and 540. The inner-region cross section is computed with the use of an adiabatic close-coupling method of essentially full quantal more » accuracy. It is shown that the two regions can be dealt with independently, to a very good approximation, and that separately calculated cross sections for each region can be added to obtain the total capture cross section. At electron-volt energies transitions in both regions are significant. Previous calculations on the C/sup 6 +/-H 1s system have treated this avoided crossing diabatically and taken into account only the transitions occurring near R = 7.0 a.u. This pair of states has a very narrow avoided crossing (.delta.E = 2.5 x 10/sup -5/ a.u.) at R = 21.36 a.u. The potential curve of the primary trajectory is the diabatic curve defined from the electronic potential-energy curves labeled 540 and 650 in united-atom notation. Transitions occur predominantly in these regions. and Rapprox.21.4 a.u., where potential curves of states leading to electron capture approach very closely the potential curve which characterizes the primary trajectory from the initial H 1s channel. There are two well-separated regions of the internuclear separation R, Rapprox.7.0 a.u. The overall energy of this nucleus would be reduced if a proton could somehow transform itself into a neutron.At electron-volt energies the probability of electron capture in C/sup 6 +/-H 1s collisions is small. Its filled energy levels would look like the well on the left. Well, nature allows this transformation and we call it - decay!Īs another example, consider 18F, which consists of 9 neutrons and 9 protons. The overall energy of the nucleus would be reduced (and its stability increased) if the “stray” neutron at the top of the neutron well could somehow transform itself into a proton and jump down to the lower energy state in the proton well. The filled energy levels would look like the well on the left. Both beta-plus and beta-minus, if allowed, always dominate electron capture since electron capture involves the relatively rare occurrence of a sizable overlap between electron and proton wavefunctions.īeta decay can be understood conceptually by looking carefully at the differences in the potential wells for protons and neutrons, and the order in which the available energy levels are filled.įor example, consider 24Na, which consists of 13 neutrons and 11 protons. The exception to this rule involves electron capture. If more than one decay involves a positive Q, the one that releases the most energy will typically dominate. Therefore, 81Kr will decay via electron capture, and release 0.281 MeV of energy per decay.
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