engleski

Two-electron capture by fast highly charged ions with emission of a single photon

Two electron capture with emission of a single photon (TESP) is a radiative process in which two electrons are captured into a bound state of an ion with emission of single photon. This process has recently been studied both experimentally and theoretically in situations in which fast heavy and highly charged ions, of charge Z_P, are collided with light targets in which electrons are relatively weakly bound (in a field of charge Z_T). In such circumstances, the TESP process has been viewed as time reversal of the double ionization process by absorption of a high energy photon, but in the specific kinematics in which both electrons are leaving atom with the same momenta, and neglecting the dependence of the TESP process on the initial electron state packing (probability to find the two electrons in the reaction region). We study TESP process for fast (velocity V) highly charged ions in the situations Z_T much smaller than Z_P. Starting from the realistic situation in which the two electrons are bound in a field of nucleus of charge Z_T, and we are able to factorize out, M_T the dependence of the TESP matrix matrix element on the packing of the initial state electrons (dependence on Z_T) while the remaining factor M_P can be treated as a time reversal of double ionization photoabsorption in a kinematics in which the two electrons leave the atom with nearly the same momenta. In treating M_P we apply time reversal and calculate matrix element for double ionization M_DI using our general nonrelativistic approach in which the dominant contributions to the matrix element for ionization by photoabsorption is associated with singularities of the Coulombic potential in specific kinematics. Using this approach we are able to distinguish contributions determined by the e-e singularity and by the e-N singularity, and discuss separately their energy dependence and Z_P dependence. In addition to the Z_P dependence which is common for the double ionization and (through time reversal) for double capture mechanisms, we find very strong Z_T^3 dependence of the TESP processes (unlike the single electron capture which does not have such strong Z_T dependence) which implies that only relatively strongly bound target electrons are involved in the two electron capture.

two electron

nije evidentirano