Ortho and para hydrogen are two spin isomers, or forms, of molecular hydrogen (H2), differing in the relative orientations of their nuclear spins. Ortho hydrogen has parallel spins, while para hydrogen has antiparallel spins. The energy difference between these isomers leads to distinct chemical and physical properties. Ortho hydrogen is more reactive and has a higher energy level, while para hydrogen is more stable and has a lower energy level. Researchers including Frederick Lindemann, Rudolph Ladenburg, Irving Langmuir, and Harold Urey played key roles in their discovery and characterization. Ortho and para hydrogen find applications in chemistry, physics, and industrial processes, such as NMR spectroscopy, fuel cells, and rocketry.
