The existence of the classical Thomas peak in the angular distribution of projectiles undergoing capture in collisions of 5-MeV protons with atomic hydrogen is explored using the three-body, three-dimensional classical-trajectory Monte Carlo technique. A method that selects only that portion of the initial phase space which yields capture at this energy was developed to make the calculation tractable due to the extremely small cross section. The spectrum obtained displays only a small shoulder near the angle predicted by Thomas on the basis of successive classical binary collisions and the total (integral) cross section is overestimated by a factor of 26 compared to recent experimental measurements. The overestimation originates from too large a contribution from velocity matching direct capture; the energy regime in which it is significant is discussed. In addition, the double-scattering events in this model which contribute significantly to the cross sections are found to differ substantially from the Thomas picture. © 1992 The American Physical Society.



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01 Jan 1992

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