【正文】 在電離過程中碰撞的理論 摘要 我們回顧過去和現(xiàn)在正子原子在電離過程中碰撞理論的發(fā)展。 碰撞動力學(xué) 。 正電子沖擊 。 三體問題比二體問題更加復(fù)雜難懂 , 除了一些特殊的現(xiàn)象，它不能被簡單的分析解 決。例如 , 在大量的中心參考系統(tǒng)下 , 我們在 1836 年描述三體問題由任何空間座標都可能的原因已經(jīng)由杰庫比介紹。 （ 2）對于電子和正子原子碰撞 , 一個微粒 (目標中堅力量 ) 比其它兩個原子要重的多。 問題的這些簡單化被介紹了在 18 世紀。 這略計廣泛被應(yīng)用在電子或正子原子電離碰撞。 因而 , 擱置一邊三個片段的內(nèi)部結(jié)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。 獨立可變物一個相似的選擇是標準的為原子電離的描述由電子沖擊 , 理論上和實驗性地 [ 3,4 ] 。 例如 , 我們也許任意地制約自己描述 coplanar (. = 0) 或 a collinear motion (. = 0 and θ1 = θ2), 以便使問題的依賴性降低到三或二獨立可變物 , 各自地。 3. 單個微粒的動量分布 動量發(fā)行為散發(fā)的電子和正子禮物幾個結(jié)構(gòu)。 終于 , 有尖頂和 anticusp 在零速度在電子和正子動量分布 , 各自地。 但是 , 我們必須記住 , 分析只微粒的當中一個在最后狀態(tài)的任一個實驗性技術(shù)可能只提供部份洞察入電離過程。 履行這個宗旨它是必要的有一種充分的量子機械治療能同時應(yīng)付電離碰撞由重和輕的子彈頭的沖擊是因此相等地可適用的 例如 對離子原子或正子原子碰撞。 如同我們解釋了 , 在離子原子碰撞 , internuclear 互作用不充當實際在散發(fā)的電子的動量發(fā)行的角色和因此未被考慮在對應(yīng)的演算。 為了是一致的與動力學(xué)的我們充分的治療 , 它是必要描述最終狀態(tài) W f 通過考慮所有互作用在同 35 樣立足處的 wavefunction 。 另外 , Garibotti 和 Miraglia 忽略了互作用潛力的矩陣元素在接踵而來的子彈頭和目標離子之間 , 并且做銳化的略計評估轉(zhuǎn)折矩陣元素。 我們選擇作為二個 獨立參量散發(fā)的電子動量組分 , 平行和垂線對正子子彈頭的行動的最初的方向。 它對應(yīng)于電子捕獲于連續(xù)流 (ECC) 尖頂被發(fā)現(xiàn)在離子原子碰撞三十年前由Crooks 和 Rudd [ 8 ] 。 因為 ECC 尖頂 是一個推測橫跨捕獲電離極限入高度激動的一定的狀態(tài) , 這個同樣作用必須是存在在正子原子碰撞。 并且這一定是如此。 Kover 和 Laricchia 測量了在 1998 dr/dEedXkdXK 橫剖面在一個 collinear 情況在零的程度 , 為 H2 的電離分子由 100 keV 正子沖擊 [ 10 ] 。 他們第一次測量了四倍有差別 37 的電離橫剖面在 collinear 幾何為離子原子碰撞 , 并且發(fā)現(xiàn) ECC 尖頂和在正子沖擊在大角度。 每個這 些過程包括正子電子二進制碰撞 , 被偏折跟隨被 90 輕的微粒的當中一個被重的中堅力量。 但有其它結(jié)構(gòu) , 在大約 。 想法是 , 電子能從離子原子碰撞涌現(xiàn)由在在子彈頭和殘余的目標離子潛力的備鞍點。 能量和動量保護原則的應(yīng)用表示 , 正子偏離在角度 終于 , 為電子涌現(xiàn)在方向和正子一樣 , 它必須遭受隨后碰撞以殘余中堅力量在 a 托馬斯象過程。 圖 3 和圖 4 精確地設(shè)置早先條件在任何能量和角度三個微粒符合的那些點。 39 圖 5 8. 結(jié)論 總結(jié)結(jié)果提出了在這通 信 , 我們由正子的沖擊調(diào)查了分子氫的電離。 終于 , 有被解釋對象由于所謂的 備鞍點 電離機制的極小值。 Collision dynamics。 Positron impact。 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] 41 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–pla–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 nieenth 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 cross section A kinematically plete description of a threebody continuum finalstate in any atomic collision would require, in principle, the knowledge of nine variables, such as the ponents of the momenta associated to each of the three particles in the final state. However, the condition of momentum and energy conservation reduces this number to five. Furthermore, whenever the initial targets are not prepared in any preferential direction, the multiple differential cross section has to be symmetric by a rotation of the threebody system around the initial direction of motion of the projectile. Thus, lea。 Wannier。 Electron spectra。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。 你是知名的電子捕獲對連續(xù)流峰頂。 圖 5 表示 , 結(jié)構(gòu)完全出現(xiàn)從 tp 期限。 這個機制被描述在圖 4.