Can Hydrocarbon Chains Be Disrupted by Fast O(3P) Atoms?

Abstract

O(3P) is a highly reactive species which may cause damage to materials on contact. In low Earth orbit (LEO), high-energy collisions (∼4.5 eV) of O(3P) with spacecraft materials can lead to extensive degradation. In this study, we use ab initio molecular orbital calculations to investigate the possibility of chain breaking in polyethylene caused by a single O(3P) attack under LEO conditions, because the occurrence of such reactions could greatly accelerate the erosion. The smallest alkanes (n = 2, 3, 5, or 7) serve as models of polyethylene. For the case of ethane (n = 2), we explore the triplet potential energy surface of the following reaction: O(3P) + CH3−CH3 → ·O−CH3 + ·CH3. Analogous reactions, in which O(3P) attacks a central carbon atom, are studied for the higher alkanes. Results obtained using the Hartree−Fock method, density functional theory, and, in the simplest case (i.e., ethane), second-order Möller−Plesset perturbation theory, Gaussian theoretical models (G1, G2, and G2MP2), and complete basis set (CBS-QB3) approaches are reported. We conclude that conditions in LEO are conducive to chain breaking in polyethylene caused by a single O(3P) attack.