Direct NO₂ formation from N₂-O₂ supercritical fluid plasma

We demonstrate a direct synthesis of nitrogen dioxide (NO₂) in supercritical nitrogen–oxygen fluid mixtures using laser-produced plasma. A tightly focused nanosecond laser pulse generates a high-density plasma that initiates chemical reactions inaccessible under ambient conditions. Time-resolved emission and absorption spectroscopy confirm the in-situ formation of NO₂, and a parametric study of input energy and gas composition reveals that plasma characteristics play a critical role in determining the reaction outcomes. This one-step process offers a compact and efficient alternative to conventional NO₂ production methods, which typically rely on the catalytic oxidation of ammonia. The use of supercritical fluids provides a unique reaction environment that enables highly selective molecular synthesis. These findings open new opportunities for deployable plasma chemical reactors in contexts such as space exploration and decentralized chemical manufacturing.