Multiple ionization of diatomic molecules by protons and multicharged ions

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

Rosario

Conferencia; XXIV International Conference on Photonic, Electronic and Atomic Collisions; 2005

Multiple ionization of diatomic molecules has been a subject of active research during recent years (see for example [1] and references therein). Particular interest was focussed on the dependenceof emission spectra with the molecular orientation [2,4]. Besides its theoretical interest as one of the basic collision phenomena, there are numerous applications for which ionization cross sections for specific targets are needed. Some of these areas of study are stellar and upper atmospheric work, radiation damage in solids, thermonuclear fusion, health physics, and plasma physics. The aim of the present work is to study this orientation dependence for different collision systems. The target molecule is described as two independent atoms separated by the equilibrium internuclear distance. The independent electron model is employed in order to describe the dynamical evolutions of electrons. A binomial distribution is considered to calculate the probability of q-fold ionization [6]. Impact parameter probabilities for single-ionization of the different atomic orbitals are represented by the exponential law $p_{i}(b)=p_{0i}exp(-b/r_{i})$, where the impact parameter b is taken according to the atomic center from wihich ionization is produced and $p_{0i}$ is the probability at zero impact parameter. In this treatment, the $p_{0i}$ is obtained by fitting single ionization total cross sections for each atomic orbital to the corresponding ones calculated with the CDW-EIS model.The radius $r_{i}$ for each atomic orbital is taken according to Hartree-Fock calculations [7]. Effective radii are also obtained using the expression $r_{i}=n_{i}/sqrt{-2 e_{i}}$, which results from a coulombic representation of the atomic orbital potential and the use of the Bohr radius formula. $e_{i}$ is the Roothaan-Hartree-Fock atomic orbital energy [8], and $n_{i}$ the corresponding principal quantum number.Differential and total cross sections for multiple ionization of CO, N$_{2}$ and O$_{2}$ targets are compared with experimental data and with predictions of other theoretical models.[1] Rivarola and Fainstein, NIMB 205, 448 (2003).[2] Wohrer and Watson, Phys. Rev. A 48, 4784 (1993).[3] Horvat et al., NIMB 99, 94 (1995).[4] Caraby et al., Phys. Rev. A 55, 2450 (1997).[5] Siegmann et al., Phys. Rev. A 65, 010704 (2001).[6] Kirchner et al., Phys. Rev. A 65, 042727 (2002).[7] Froese Fischer, ADNDT 4, 301 (1972).[8] Clementi and Roetti, 14, 177 (1974).