Water-vapor-based source of UV radiation

The results of studying a capacitive discharge in water vapor are reported. This discharge is an effective and environmentally friendly source of UV radiation due to hydroxyl OH (A ²Σ⁺ → X ²Π transition) in the wavelength range 280–330 nm. It is shown that, at E/N < 210 Td, the discharge is greatly influenced by dissociative attachment of electrons, while at E/N > 210 Td, ionization dominates over dissociation. The formation rate of excited OH* radicals (A ²Σ⁺) in the water-vapor discharge is much higher than the formation rate of emitting states in hydrogen and oxygen atoms. As E/N grows, the ratio between the intensities of OH lines and atomic hydrogen Balmer series decreases. According to estimates, E/N values optimal for the OH radical line excitation fall into the range 250–400 Td.