, Volume 48, Issue 1, pp 177-184

Mechanisms of inelastic scattering of low-energy protons by C6H6, C60, C6F12, and C60F48 molecules

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Abstract

The mechanisms of inelastic scattering of low-energy protons with a kinetic energy of 2–7 eV by C6H6, C6F12, C60, and C60F48 molecules are studied using the methods of quantum chemistry and nonempirical molecular dynamics. It is shown that, for the C6H6 + proton and C60 + proton systems, starting from a distance of 6 Å from the carbon skeleton, the electronic charge transfer from the aromatic molecule to H+ occurs with a probability close to unity and transforms the H+ ion into a hydrogen atom and the neutral C6H6 and C60 molecules into cation radicals. The mechanism of interaction of low-energy protons with C6F12 and C60F48 molecules has a substantially different character and can be considered qualitatively as the interaction between a neutral molecule and a point charge. The Coulomb perturbation of the system arising from the interaction of the noncompensated proton charge with the Mulliken charges of fluorine atoms results in an inversion of the energies of the electronic states localized, on the one hand, on the positively charged hydrogen ion and, on the other hand, on the C6F12 and C60F48 molecules. As a result, the neutral molecule + proton state becomes the ground state. In turn, this inversion makes the electronic charge transfer energetically unfavorable. Quantum-chemical and molecular-dynamics calculations on different levels of theory showed that, for fluorine derivatives of some aromatic structures (C6F12, C60F48), the barriers to proton penetration through carbon hexagons are two to four times lower than for the corresponding parent systems (C6H6, C60). This effect is explained by the absence of active π-electrons in the case of fluorinated molecules.