Ionization of biological molecules by multicharged ions using the stoichiometric model

Abstract

In the present work, we investigate the ionization of molecules of biological interest by the impact of multicharged ions in the intermediate to high energy range. We performed full non-perturbative distorted-wave calculations (CDW) for thirty-six collisional systems composed by six atomic targets: H, C, N, O, F and S -which are the constituents of most of the DNA and biological molecules-and six charged projectiles (antiprotons, H, He, B, C, and O). On account of the radiation damage caused by secondary electrons, we inspect the energy and angular distributions of the emitted electrons from the atomic targets. We examine seventeen molecules: DNA and RNA bases, DNA backbone, pyrimidines, tetrahydrofuran (THF), and CnHn compounds. We show that the simple stoichiometric model (SSM), which approximates the molecular ionization cross sections as a linear combination of the atomic ones, gives reasonably good results for complex molecules. We also inspect the extensively used Toburen scaling of the total ionization cross sections of molecules with the number of weakly bound electrons. Based on the atomic CDW results, we propose new active electron numbers, which improves significantly scaling for all the targets and ions studied here in the intermediate to the high energy region. The new scaling describes well the available experimental data for proton impact, including small molecules. We perform full molecular calculations for five nucleobases and test a modified stoichiometric formula based on the Mulliken charge of the composite atoms. The difference introduced by the new stoichiometric formula is less than 3%, which indicates the reliability of the SSM to deal with this type of molecules. The results of the extensive ion-target examination included in the present study allow us to assert that the SSM and the CDW-based scaling will be useful tools in this area.

Atomic ionization by multicharged ions interpreted in terms of poles in the velocity complex space

“…To interpret the cross section we introduce a diagonal Padé approximant. We find that the use of a Padé [4,4] describes the continuum distorted wave eikonal initial state theory within its range of validity very well. The nodes of the denominator of the Padé approximant give rise to four poles in the velocity complex plane: two in the upper plane and their conjugates in the lower plane.…”

“…This potential reads 8) in terms of v/v max . (d) The relative error of σ [4,4] versus the CDW values, as defined in equation (22) in terms of v/v max .…”

“…Therefore, the challenge of dealing with large Z has resurfaced, but now within the more complex field of molecular targets. To deal with this challenge, some models reduce the problem to a sum of ionization cross sections of the atoms composing the molecules [4]. More refined approaches also take into account the geometry of the molecule, but still the problem of dealing with high Z persists.…”

A Complete CDW Theory for the Single Ionization of Multielectronic Atoms by Bare Ion Impact

“…With the above choice given in (8) for φ f , the function Φ f in (5) is, therefore, the solution of the Schrödinger equation:…”

“…This allowed the extension of these distorted theories to complex electronic systems. Since that time, they were used in a reliable way to calculate the differential, as well as the total cross-section for a wide variety of collision systems with projectiles ranging from antiprotons to highly-charged bare ions and targets going from atoms to a large diversity of molecules [3][4][5][6][7][8][9]. In the distorted wave formalism, the action of the perturbative potentials can either be applied to the initial channel distorted wave function or to the final channel distorted one, giving place to the prior and post versions of the transition matrix element, respectively [10,11].…”