Multiple electron emission in ion-molecule collisions including post-collisional effects

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

Freiburg

Conferencia; XXV International Conference on Photonic, Electronic and Atomic Collisions; 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 (radiative 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 biological physics. For example, postcollisional 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 autoionization probabilities for atomic target with nuclear charge Z less than 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 postcollisional electrons for atoms with Z less than 10 and to analyze the influence of this type of processes on the total multiple ionization cross sections for impact of ions on diatomic molecules. To this end, we work within the framework of the Independent Particle Model (IPM) to describe the 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, showing the relevance of Auger type mechanisms at high impact energies, as it happens for atomic targets [4].[1] Kobayashi et al., NIMB 199, 348 (2003).[2] Carlson et al., Phys. Rev 151, 41 (1966).[3] Simsek, Phys. Rev. A 62, 052517 (2000).[4] Spranger and Kirchner, J. Phys. B 37, 4159 (2004).[5] Sant'Anna et al., Phys. Rev. A 58, 2148 (1998).[6] Wells et al., Phys. Rev. A 72, 022726 (2005).