67- Multiple ionization cross sections by ion impact on Ne-like molecules

B. GERVAIS; V. TESSARO; M. GALASSI; M. BEUVE

Caen

Conferencia; 10th International Symposium on Swift Heavy Ions in Matter (SHIM) & 28th International Conference on Atomic Collisions in Solids (ICACS); 2018

Université de Caen - Basse Normandie

The study of multiple ionization of molecules by swift ion impact is of great interest in many subfields of physics, chemistry, astrophysics and ion-beam cancer therapy. During the irradiation of human tissues with such ions, the biological molecules are ionized and excited. Mainly, in the region of maximum energy deposition (known as the Bragg?s peak), multi-electron processes occur (transfer-ionization, multiple ionization, etc). Experimental cross sections for multi-electron emission by heavy ion impact on molecules are scarce and the development of predictive accurate theoretical models to calculate multiple-ionization cross sections (MICS) is necessary. In previous works, exclusive MICS of water molecules by ion impact were calculated in the framework of the Independent Particle Model (IPM), employing a binomial distribution in order to take into account contributions from different molecular target orbitals. The single particle probabilities as a function of the impact parameter were calculated using two different methods: the Exponential Model (EM) and the Continuum Distorted Wave - Eikonal Initial State (CDW-EIS) approximation [1-2]. Within the Exponential Model, it is assumed that the atomic and molecular orbitals present a spherical shape centered in the oxygen atom in the case of the water molecule. The single-electron emission probabilities for each shell are described by decreasing exponential functions with adjustable parameters to reproduce CDW-EIS net-ionization cross sections. For the case of proton impact on Ne and Ar, MICS-EM was found in remarkable agreement with experimental data [3]. In the present work, we extend the use of the MICS-EM to monocentric Ne-like molecules (H2O, CH4, NH3). The post-collisional contributions, that dominates the MICS at high impact energy, is considered by extending the model used for Ne [2]. We analyze the dependence of multiple ionization cross sections with the energy and charge of the projectile. For these light molecules good agreement with experimental data is obtained. References[1] B. Gervais, M. Beube, G. Olivera and M. Galassi. Rad. Phys. Chem. 75, 493-513 (2006).[2] R. D. Rivarola, M. E. Galassi, P. D. Fainstein, C. Champion. Book series "Advances in Quantum Chemistry: Theory of heavy ion collision physics in hadron therapy". Chapter nine.Editorial: Elsevier Inc. Copenhagen, Dinamarca. Editor: Dzevad Belkic. (2013).[3] M.E. Galassi, R.D. Rivarola and P.D. Fainstein. Phy. Rev. A 75, 052708 (2007).