【正文】 構(gòu)在最終狀態(tài), 只四 喪失九可變物是必要完全地描述驅(qū)散過程。 例如, 我們也許任意地制約自己描述coplanar (. 前廣泛被應用學習電子碰撞, 當后者是主要工具描繪離子原子和正子原子電離碰撞。秒鐘是取盡由于正子的捕獲的不可能的事由目標中堅力量。 特別是, 它會允許我們學習變異當改變在二之間制約了運動學情況。 在連續(xù)流波浪作用這個選擇的最后渠道擾動潛力是[ 5 ]在純凈的庫侖潛力情況下, 畸變被給關(guān)于這個模型由佳瑞波帝和馬瑞吉拉[ 6 ] 提議為離子原子碰撞, 并且由Brauner 和布里格斯六年后為正子原子和電子碰撞[ 7 ] 。圖2, 我們觀察三個不同結(jié)構(gòu): 二個極小值和土坎。 這爭執(zhí)的原因是那, 與離子對比盒, 正子外出的速度與那不是相似沖擊, 但主要傳播在角度和巨大。 從目標反沖不充當在這個實驗性情況的重大角色, 當前一般理論給結(jié)果相似與那些由Berakdar [ 11 ] 獲得, 并且兩個跟隨嚴密實驗性價值。 在這種情況下, 從電子和正子大量是相等的, 這兩個過程干涉在45 。 在 離子原子碰撞案件, 查尋這個機制的理論和實驗性證據(jù)是陰暗由生動的爭論[ 1418 ] 。 圖5 表示, 結(jié)構(gòu)完全出現(xiàn)從tp 期限。橫剖面也許會被很多巨大的困難所阻礙, 但值得高興的是, 我們一直沒有錯過對問題許多不同的全方位的觀察, 唯一的遺憾就是對總橫剖面的研究。 Wannier。θ2), so as to reduce the dependence of the problem to three or two independent variables, respectively. The other option is to integrate the quadruple differential cross section over one or more variables.The former has been widely used to study electron–atom collisions, while the latter has been the main tool to characterize ion–atom and positron–atom ionization collisions. Particularly important has been the use of single particle spectroscopy, where the momentum of one of the particles is measured. 3. Single particle momentum distributions In ionization by positron impact it is feasible to study the momentum distribution of any of the involved fragments. As is shown in Fig. 1, the momentum distributions for the emitted electron and the positron present several structures. First, we can observe a threshold at high electron or positron velocities because there is a limit in the kinetic energy that any particle can absorb from the system. The second structure is a ridge set along a circle. It corresponds to a binary collision of the positron with the emitted electron, with the target nucleus playing practically no role. Finally, there is a cusp and an anticusp at zero velocity in the electron and positron momentum distributions, respectively. The first one corresponds to the excitation of the electron to a lowenergy continuum state of the target. The second is a depletion due to the impossibility of capture of the positron by the target nucleus. These momentum distributions allow us to study the main characteristics of ionization collisions. However, we have to keep in mind that any experimental technique that analyzes only one of the particles in the finalstate can only provide a partial insight into the ionization processes. The quadruple differential cross sections might display collision properties that are washed out by integration in this kind of experiments. Fig. 1.Vi Ψi and (HQDCS for ionization of H2 by impact of 1dΩkE)Ψf= 1. Introduction The simple ionization collision of a hydrogenic atom by the impact of a structureless particle, the “threebody problem”, is one of the oldest unsolved problems in physics. The twobody problem was analyzed by Johannes Kepler in 1609 and solved by Isaac Newton in 1687. The threebody problem, on the other hand, is much more plicated and cannot be solved analytically, except in some particular cases. In 1765, for instance, Leonhard Euler discovered a “collinear” solution in which three masses start in a line and remain linedup. Some years later, Lagrange discovered the existence of five equilibrium points, known as the Lagrange points. Even the most recent quests for solutions of the threebody scattering problem use similar mathematical tools and follow similar paths than those travelled by astronomers and mathematicians in the past three centuries. For instance, in the centerofmass reference system, we describe the threebody problem by any of the three possible sets of the spatial coordinates already introduced by Jacobi in 1836. All these pairs are related by lineal point canonical transformations, as described in [1]. In momentum space, the system is described by the associated pairs (kT,KT), (kP,KP) and (kN,KN). Switching to the Laboratory reference frame, the final momenta of the electron of mass m, the (recoil) target fragment of mass MT and the projectile of mass MP can be written in terms of the Jacobi impulses Kj by means of Galilean transformations [1]For decades, the theoretical description of ionization processes has assumed simplifications of the threebody kinematics in the final state, based on the fact that ? in an ion–atom collision, one particle (the electron) is much lighter than the other two,? in an electron–atom or positron–atom collision, one particle (the target nucleus) is much heavier than the other two.For instance, based on what is known as Wick’s argument, the overwhelming majority of the theoretical descriptions of ion–atom ionization collisions uses an impactparameter approximation, where the projectile follows an undisturbed straight line trajectory throughout the collision process, and the target nucleus remains at rest [2]. It is clear that to assume that the projectile follows a straight line trajectory makes no sense in the theoretical description of electron or positron–atom collisions. However, it is usually assumed that the target nucleus remains motionless. These simplifications of the problem were introduced in the eighteenth century. The unsolvable threebody problem was simplified, to the socalled restricted threebody problem, where one particle is assumed to have a mass small enough not to influence the motion of the other two particles. Though introduced as a means to provide approximate solutions to systems such as Sun–planet–et within a Classical Mechanics framework, it has been widely used in atomic physics in the socalled impactparameter approximation to ion–atom ionization collisions. Another simplification of the threebody problem widely employed in the nineteenth century assumes that one of the particles is much more massive than the other two and remains in the center of mass unperturbed by the other two. This approximation has been widely used in electron–atom or positron–atom ionization collisions. 2. The multiple differential cro