Multiple ionization of diatomic molecules by protons and multicharged ions

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

Rosario, Argentina

Conferencia; 24 International Conference on Photonic, Electronic and Atomic Collisions (XXIV ICPEAC); 2005

Grupos de Colisiones Atómicas de Rosario-Buenos Aires y Bariloche

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 dependence of 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 speci¯c 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 di®erent collision systems. The target molecule is described as two independent atoms separated by the equilibrium internuclear molecular 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 di®erent atomic orbitals are represented by the exponential law pi(b)= p0i e¡b=ri , where the impact parameter b is taken according to the atomic center from which ionization is produced and p0i is the probability at zero impact parameter. In this treatment, the p0i value is obtained by ¯tting single ionization total cross sections for each atomic orbital to the corresponding ones calculated with the CDW – EIS model. The radius ri for each atomic orbital is taken according to Hartree – Fock calculations [7]. E®ective radii are also obtained using the expression ri = ni=p¡2 "i, which results from a coulombic representation of the atomic orbital potential and the use of the Bohr radius formula. "i is the Roothan – Hartree – Fock atomic orbital energy [8], and ni the corresponding principal quantum number. Di®erential and total cross sections for multiple ionization of CO, N2, and O2 targets are compared with experimental data and with predictions of other theoretical models. References [1] R. D. Rivarola and P. D. Fainstein, Nucl. Instrum. Methods B 205, 448 (2003). [2] K. Wohrer and R. L. Watson, Phys. Rev. A 48, 4784 (1993). [3] V. Horvat, O. Heber, R. L. Watson, R. Parameswaran and J. M. Blackadar, Nucl. Instrum. Methods B 99, 94 (1995). [4] C. Caraby, A. Cassimi, L. Adoui and J. P. Grandin, Phys. Rev. A 55, 2450 (1997). [5] B. Siegmann, U. Werner, R. Mann, Z. Kaliman, N. Kabachnik and H. O. Lutz, Phys. Rev. A 65, 010704 (2001) [6] T. Kirchner, L. Guly¶as, R. Moshammer, M. Schulz and J. Ullrich, Phys. Rev. A 65, 042727 (2002). [7] C. Froese Fischer, Atomic Data and Nuclear Data Tables 4, 301 (1972). [8] E. Clementi and C. Roetti, Atomic Data and Nuclear Data Tables 14, 177 (1974).