Main species and physicochemical processes in cold atmospheric-pressure He + O₂ Plasmas

The main species and chemical processes in low-temperature atmospheric-pressure He + O₂ plasmas are identified using a comprehensive global model. The simulation results highlight the significance of Penning processes at low oxygen concentration, and the increasingly important role of electron attachment as the oxygen concentration increases. With increasing the oxygen concentration, the electron energy dissipation shifts from elastic collisions with He to dissociative excitation and attachment of O ₂ molecules, and large ions (O⁺₃, O ⁺₄) become the dominant charged species. Generation and loss of ROS (O, O(¹D), O(¹S), O₂(a ¹δ_g), O₂(b¹σg+), O ₃) relevant for biomedical applications are discussed. Cold atmospheric-pressure He+O₂ plasmas are an excellent source of reactive oxygen species (e.g. O, O(¹D), O(¹S), O ₂(a¹δ_g), O₂(b ¹σg⁺), O₃) relevant in many applications, such as plasma medicine. Here we report on a detailed analysis of the interaction among 21 species and 267 reactions involved in these plasmas and unravel the main physicochemical processes at play.