MULTIPLE ELECTRON EMISSION IN ION-MOLECULE COLLISIONS INCLUDING POST-COLLISIONAL EFFECTS

C.A TACHINO; M.E. GALASSI; R. RIVAROLA

Freiburg, Alemania

Congreso; 25 International Conference on Photonic, Electronic and Atomic Collisions (XXV ICPEAC); 2007

    The ionization of an atomic or molecular target due to a collision process creates vacancies in different shells, leading the target in a highly excited state. After a time delay, the vacancies of the most internal shells are occupied by higher shell electrons. The energy generated in this process either is released as a x-ray photon (radia-tive transition) or is transferred to another bound electron (radiationless transition, i. e., Auger or Coster-Kronig transition) which is ejected, increasing the total ionization degree of the target.    The knowledge of autoionization and radiative probabilities have great importance in a number of areas, such as astrophysics and bio-logical physics. For example, post-collisional effects are important in the interpretation of solar-flare spectra emitted by transient ionizing plasmas and in the interpretation of vacuum ultraviolet spectra of the outer atmosphere of the sun.Also, induction of autoionization processes in living matter can cause multiple damages in macromolecules that constitutes the cells [1].    The existing experimental data for autoionization rates and probabilities were obtained mainly for photon impact on noble gases [2], and to a lesser extent for photoionization of atomic targets with nuclear charge greater than 10 [3]. But to our knowledge there is neither experimental nor theoretical information on q-fold au-toionization probabilities for atomic target with Z < 10 or for molecular target.    Based on this information and on the work of Spranger and Kirchner [4], we have decided to estimate the probabilities of emission of post-collisional electrons for atoms with Z < 10 and to analyze the influence of this type of processes on the total multiple ionization cross sectionsfor impact of ions on diatomic molecules. To this end, we work within the framework of the Independent Particle Model (IPM) to describethe dynamical evolution of electrons. Binomial distributions are considered to calculate q-fold ionization probabilities [5], and impact parameter probabilities for single ionization are obtained using different approximations based on the Continuum Distorted Wave-Eikonal Initial State model.    Total cross sections including post-collisional effects for different q-ionization degrees of molecular targets are compared with existing experimental results (see for example figure 1), showing the relevance of Auger type mechanisms at high impact energies, as it happens for atomic targets [4].References[1] K. Kobayashi et al., Nucl. Inst. Methods B 199, 348 (2003).[2] T. Carlson et al., Phys. Rev 151, 41 (1966).[3] O. Simsek, Phys. Rev. A 62, 052517 (2000).[4] T. Spranger and T. Kirchner, J. Phys. B 37, 4159 (2004).[5] M. Sant’Anna et al., Phys. Rev. A 58, 2148 (1998).[6] E. Wells et al., Phys. Rev. A 72, 022726 (2005).