The dominance of Auger-type electron emission in ion-molecule collisions

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

París

Conferencia; International Conference on Many Particle Spectroscopy of Atoms, Molecules, Clusters and Surfaces 2008; 2008

As a consequence of electron ionization of a molecular target in a collision process, vacancies in different molecular orbitals are created, leading the target in a highly excited state. After a time delay, once the projectile is far away, the vacancies in the inner orbitals are filled by residual target electrons, and the excess of energy generated in this process is employed to release x-ray photons (radiative transitions) or to produce ionization of other bound molecular electrons (Auger-type emission)[1-3]. The knowledge of autoionization and radiative probabilities have great importance in different scientific areas, such as astrophysics and biological physics (see, for example, refs. [4, 5]).The existing experimental data for autoionization rates and probabilities were obtained mainly for photon impact on noble gases (see, for example, ref. [6]). To our knowledge experimental or theoretical information on q-fold autoionization probabilities (q> 1) for atomic targets such as C, N and O, or for molecular targets is scarce. Based on experimental photoionization probabilities [6] and on the work of Spranger and Kirchner [7], we estimate the importance of Auger-type emission on total multiple ionization cross sections for impact of fast proton beams on diatomic molecules. To this end, we employ the independent electron approximation and binomial distributions to calculate cross sections for q-ionization degree. The diatomic molecule is described as an ensemble of two independent atoms separated by the corresponding molecular equilibrium distance. Impact parameter probabilities for single ionization are obtained using different approximations based on the Continuum Distorted Wave-Eikonal Initial State model.By comparison with experiments it is shown that, for CO targets, Auger type emission dominates the multiple electron ionization reaction at high enough collision energies, as it was previously shown to happen with atomic targets [7-9]. [1] Auger, Compt. Rend. 177, 169 (1923). [2] Auger, Compt. Rend. 180, 65 (1925). [3] Auger, J. Phys. Radium 6, 205 (1925). [4] Kobayashi et al., NIMB 199, 348 (2003). [5] Tmneanu et al., Chem. Phys. 299, 277 (2004). [6] Carlson et al., Phys. Rev. 151, 41 (1966). [7] Spranger and Kirchner, J. Phys. B 37, 4159 (2004). [8] Galassi et al., Phys. Rev. A 75, 052708 (2007). [9] Archubi et al., J. Phys. B 40, 943 (2007).[10] Wells et al., Phys. Rev. A 72, 022726 (2005).