Scaling Law Of Helium Double Ionization For Impact By Ions From H⁺to U⁹²⁺ In Strong Coupling Regime

The mechanism of collision between ion and atom have played an important role in many fundamental areas, such as the life of ion in accelerator, atomic spectroscopy, ion transportation in the material and plasma physics. When the experimental data and theory results are not available, the scaling law of cross section in collision is very necessary. Based on our previous classical over barrier ionization (COBI) model, a universal scaling law of double-to-single ionization cross section ratios R21for impact by nearly stripped ions from H+to U92*in the strong coupling regime (0.5<q/υ<5) was found, where q is the charge state of projectile and υ is the projectile velocity.The projectile velocity can be divided into υ>>υnl and υ<<υnl.When the velocity of projectile is much greater than the orbital velocity of the target electrons, the electrons are " stationary ". The projectile interact with the static electron directly, hence, the Born Approximation is always used to obtain the cross sections. The ionization dominate the entire process. On the other hand, when the velocity of projectile is much smaller than the velocity of the target electrons, the initial velocity of the electrons have to be taken into account. The exchange effect of charge is so more important that the electron is captured by the projectile easier rather than be ionized directly.Regarding strong couple regime, when the velocity of the projectile is comparable with the orbital velocity of the target electron, the ionization and capture processes will occur simultaneously. The theories and experiments are relatively rare. In this work, we proposed that the direct ionization of released electron will dominate the entire processes. Based on COBI, the scaling law is obtained, which is consistent with extensive experimental data ranging from H+to U92+. A fitting curve to the predictions of the theory is also proposed for application convenience.