Reaction dynamics of antiprotonic hydrogen formation in collisions between antiprotons and molecules

用波包传输全量子力学方法或量子经典混合(即半经典)近似方法研究了低能反质子与原子或分子离子的碰撞。研究发现，绝热图像(即Born-Oppenheinmer分离)在很大程度上是合适的。对于原子离子靶，反质子俘获是一个典型的非绝热过程，因为在这个过程中必须发射电子，因此发生频率较低。然而，即使在非常低的能量下，捕获几率实际上很小，但对于大的角动量仍然是有限的。相应地，非绝热过程的截面在零能极限内发散。这是由于库仑力范围比离心力范围大的特点造成的。在分子离子靶的情况下，绝热条件得到了更好的满足，因为t…更多的氦电子可以通过形成中性原子或分子从反质子中逃逸。同时，即使在绝热近似下，也有可能形成多孔性原子。对于分子离子靶，反质子原子的形成可以处理为单个绝热(Born-Oppenheimer)势能面(PES)上的碰撞，其方式与化学反应问题相同。计算了反质子和氢分子离子体系的电子能谱。碰撞计算采用经典的轨迹蒙特卡罗方法。发现解离动力学在反质子氢(质子)的形成中起着关键作用，因此分子靶在反质子捕获方面比原子靶更有效。我还计算了氢分子离子与负介子和负介子的碰撞，并研究了质量效应对反应动力学的影响。结果表明，反质子俘获具有显著的质量依赖性。这显然与可以忽略不计的大规模依赖形成对比。这显然与原子对反质子俘获的微不足道的依赖性形成了鲜明的对比，在这种依赖中，非绝热耦合起着主导作用。较少

Low-energy antiproton collisions with atomic or molecular ions was investigated using a wave-packet-propagation full-quantum-mechanical method or a quantum-classical hybrid (i.e., semiclassical) approximation. It is found that the adiabatic picture (i.e., Born-Oppenheinmer separation) is appropriate in a large sense.In the case of atomic ion targets, the antiproton capture is a typical non-adiabatic process because the electron must be emitted in this process, and hence occurs less frequently. However, even at very low energies, the capture probability is in fact small but finite still for large angular momenta. Correspondingly, the cross section for the non-adiabatic process diverges in the zero energy limit. This happens due to the peculiarity that the Coulomb force range is longer than the centrifugal one. Importance of a Rydberg series of resonances in the capture process is also 0found.In the case of molecular ion targets, the adiabatic condition is satisfied much better because t … More he electron can escape from the antiproton by forming a neutral atom or molecule. At the same the, the formation of aniti porotonic atoms becomes possible even in the adiabatic approximation. For the molecular ion targets, the antiprotonic atom formation can be treated as the collisions on a single adiabatic (Born-Oppenheimer) potential energy surface (PES), in the same manner as chemical reaction problems. The PES was caclculated for teh antiproton and hydrogen molecular ion system. A classicla trajectory Monte Carlo method was applied to the collision calculation. It is found that the dissociative dynamics plays a critical role in antiptotonic hydrogen (protonium) formation, the consequently the molecular target is much more effective in antiproton capture than the atomic target.I carried out the calculation also for collisions of hydrogen molecular ions with negative muons and kaons, and investigated the mass effect on the reaction dynamis. It is found that the antiproton capture has a remarkable mass dependence. This is clearly in contrast to the negligible mass dependence. This is clearly in contrast to the negligiblemass dependence of the antiproton capture by atom in which the non-adiabatic coupling plays a dominant role. Less