Experimental Investigation Of Collision Dynamics In Transfer Ionization Of He₂₊Collisions With Argon Atom

Using well developed cold target recoil ion momentum spectroscopy (COLTRIMS), state selective electron capture and electron emission mechanisms in the transfer ionization of He2+collision with argon have been investigated. The longitudinal recoil ion momentum distribution, electron distribution in and out of the scattering plane, and differential cross section of electron ejected in T1I1, T2I1and T1I2have been obtained.Our results show that quasi-resonant capture mechanism leads to the preference of the first excited state of He+for the single capture process, and the singly excited state of He for the double capture process, respectively. In T1I1process, it is demonstrated that the fruitful mechanisms contributing to the electron emission including direct transfer ionization (DTI), double-electron capture followed by auto-ionization (DECA), single-electron capture with Auger (SECA) of target, and cusp electron emission. The low energy resonant structures show that Ar+in SECA decays mainly through the3s3p53d by emitting Auger electrons, and doubly excited He mainly decays through the2l2l states. In the transfer ionization process studied here, the DTI process dominates the low energy electron emission, and there is no prominant saddle-point electron emission. Further, we have investigated the potential physical mechanism behind cusp electron emission by the presented TCS of cusp electrons (toal cross sections) for collision energies from17.5keV/u to75keV/u. We find a maximum of TCS at the projectile energy of30keV/u, which coincide with the prediction of velocity matching between the projectile ion and the electron initially bound to the target. One of the important issues for T1I1is the role of electron-electron correlation, our experimental and theoretical results indicate that electron-electron correlation is ignorable, the independent and sequential two steps of first single ionization followed by single electron capture dominates the cusp electron emission. However, single capture followed by single ionization also makes a non-negligible contribution, simultanoesuly target are excited.In T2I1processes, our results show that there is no cusp peak in the forward spectrum of DDCS. For the T1I2processes, two electrons eject with approximately same longitudinal momentum due to the couloumb attraction. For small energy electrons, the strongly final repulsion leads to a "back to back" scenario, which indicates final electron-electron correaltion.